Written by Ashley Cowie. First published 02 July 2016 - republished 06 January 2024.

Abstract: Following an interpretation of the astronomical and cosmological themes expressed in the architecture of Cambodia's Angkor Wat temple complex, a potentially significant 10th-century dynastic prime meridian is delineated, and its use in determining the precise location of Angkor Wat is posited.

Keywords: Khmer, Vedic, Mythology, Cosmology, Sacred Geography, Astronomy, Geometry, Hindu Architecture, Mandala, Cambodia, Meridian.

Accompanies: Episode 1 of the History Fuzz podcast with Professor Giulio Magli.

Cosmic Khmer Centres

In 1998 the “International Journal of Historical Archaeology” published a research paper by David Welch titled“Archaeology of Northeast Thailand in Relation to the Pre-Khmer and Khmer Historical Records.” Welch stated that between 879 - 1191 CE the Angkor Empire encompassed “a vast territorial expanse stretching from contemporary southern Vietnam to Yunan, China, and extending westward to the Bay of Bengal.” [1]

Constructed between 1113 - 1150 CE, during the reign of Emperor Suryavarman II, the expansive Hindu temple complex, Angkor Wat, situated in present-day Cambodia, is an architectural marvel unparalleled in scale elsewhere on Earth. Covering an area of approximately 162.6 hectares (1,626,000 square meters or 402 acres), the 2010 publication “Angkor, Cambodia. Asian Historical Architecture” described the sacred super-structure as “the world's largest religious monument.” [2] During the same historical period, London, England, supported a populace numbering around 18,000 individuals, while the Angkor region housed more than one million inhabitants. [3]

While the leaders of mainstream Western religions build congregational gathering spaces for prayer and sermons, in contrast, according to author Michel Freeman in his 1990 paper “Angkor,” Khmer temples represent “the totality of the Hindu cosmological universe, offering a path to transcendence from perpetual suffering and rebirth through rituals.” [4]

The design principals underlying Hindu temples was discussed in the 1981 book “Bodhisattva Doctrine in Buddhism” which describes the apex of spiritual transcendence in Buddhism as “Nirvana,” or “Moksha,” in the context of Hinduism. This enlightened state of being was attained “at the central sanctum of Khmer temples,” and in order to facilitate and amplify this profound spiritual encounter, temple ground plans across Southeast Asia were derived from geometric devices called “Mandalas,” which served to amalgamate cosmological, religious, and psychological motifs. [5]

Mandalas were crafted so that every proportion, space, area, ratio, length, breadth, and height carried significant symbolic associations. The mandalas foundational square framework, adorned with concentric circles and T-shaped gates on each face, collectively delineate a central focal point. Andrew Forbes and David Henley’s 2011 book “Angkor, Eighth Wonder of the World” proposes that Khmer architects "modulated the dimensions of concentric squares, circles, and triangles, expertly achieving radial equilibrium to ensure their architectural designs resonated with harmonic balance across all constituent elements”. [6]

María Mora Viñas’ 2022 book “Introducción a la psicología del mandala” explains that mandalas served as “repositories of esoteric and religious wisdom, aiding meditation and temple design.” This is because whether fingered in a box of sand or painted on papayrus, Khmer geometers grappled with a puzzling phenomenon: “no matter the scale of expansion or contraction, the central point in their designs remained fixed.” The central point in Hindu temples is known as the "garbhagriha,” and represents the cosmic centre. Thus, the innermost temple chamber, located at the garbhagriha, was perceived as the residence of deities, and as such, these structures were aligned with the cardinal directions to illustrate human interaction with the greater universe. [7]

Mircea Eliade’s 1991 book, “Symbolism of the Centre” explains that at the garbhagriha, the heart of Hindu temples, resided the "axis mundi," an imperceptible column of perceived sacred energy believed to bridge the heavens and the earth. [8] Through this divine conduit Khmer rulers were “directly united with the gods, and deities were thought to channel spiritual energy into the earthly domains, bestowing prosperity upon the kingdom.” Hence, when a ruler announced the construction of a capital city, they were essentially initiating the establishment of a new garbhagriha, an exemplary centre: a veritable generator of prosperity.

Over time mandala designs underwent significant horizontal expansion and came to encapsulate the astronomical framework of the universe within a cosmological schema. According to scholar Fritjof Schuon in his 1982 book “From the Divine to the Human: Survey of Metaphysics and Epistemology,” Khmer temple architects pioneered a transformative approach by introducing a third dimension, “vertically extrapolating reducing squares and forming stepped pyramids crowned with central towers,” representing a significant advancement in mandala mechanics and cosmic expression. [9]

In Benjamin Walker’s 1969 book, “Hinduism: Ancient Indian tradition & mythology” the author writes that this pivotal evolution in sacred architecture from the horizontal plane, which was traditionally associated with terrestrial realms, allowed for creative expressions of Hindu-Buddhist convictions that “mountains, mountain ranges, and caverns were hallowed residences of the divine”. [10] Furthermore, Angkor researcher, Dr. Soekmono, concluded his 1973 book “Pengantar Sejarah Kebudayaan Indonesia” suggesting that Angkor Wat was built upon a square ground plan comprising four towers, encompassing a central tower, "perfectly representing descriptions of Mount Meru in Hindu cosmology, the divine residence of gods”. [11]

Another key Khmer building dynamic was explored by Dr. Edwin Bernhart, who in his 2013 paper suggested “the zenith passage of the sun was exceptionally important in ancient Khmer culture,” when at noon the sun was directly overhead casting no shadow. Architectural features and orientations, art panels and monuments, all determine that the zenith passage was of the greatest importance, and this astronomical phenomenon permeates the entire city. [12] Dr. Edwin Bernhart features in Episode 8 of the History Fuzz podcast discussing his personal experience of the zenith event in a Khmer temple.

Vedic Measuring Skills

Because the mythical Mount Meru was a central theme in Hindu cosmology, Khmer architects constructed stone towers representing the snowy-peaks surrounding the divine mountain abode. However, examinations of the layouts and orientations of Khmer temples have identified many other architectural principals derived from Indian Vedic cosmology and astronomy. [13]

In 1999, a research paper was published in the “Journal of the Royal Astronomical Society of Canada” titled “A Brahmanic fire altar explains a solar equation in Angkor Wat.” The authors suggested “that in essence, the Khmer builders amalgamated key aspects of ancient Indian Vedic architectural practices, incorporating cosmological, astronomical, and philosophical elements, ultimately contributing to the unique and awe-inspiring architectural legacy of the Khmer civilization.” [14]

While stones were being cut from quarries the architects of Angkor Wat delineated their structure with posts and ropes, adhering to Vedic geometrical practices. Therefore, to gain rudimentary insights into the astronomical framework at Angkor Wat a foundational exploration into the archaic methodologies of rope craftsmanship and measurement employed by ancient Vedic Indian altar and temple builders is imperative.

In 2024, I published a book titled “Ropes and Ruins” exploring the crafts and skills associated with rope-making and measuring in prehistory. This book illuminates the transformation of rope measuring practices into formalized sciences, exploring the works of the Greek mathematicians who refined Egyptian rope measuring methods into the disciplines of geometry, mathematics and astronomy. [15]

In my book, I present research from the 2001 paper by scholar Edwin Bryant, titled “The Quest for the Origins of Vedic Culture: The Indo-Aryan Migration Debate.” The author discussed the “Sulbasutras,” an early Hindu religious tract written around 800 BCE, providing archaeological evidence pointing to an advanced knowledge of rope crafts and geometry in the pre-Vedic culture, the Harappans, which pushes the origins of formalized rope geometry on the Indian subcontinent to well before 2000 BC. [16] 

The word 'sulba' means string, rope or cord, and the closest English translation of the word 'sutras,’ is ‘codes.’ The Sulbasutras, or “rope-codes,” detail the practical skills and techniques required to measure and build in a systematic way, describing how to create Vedic ceremonial sacrificial fires at different times of the year, with astronomical accuracy. The job of identifying suitable locations for Vedi (altars), then orienting and aligning them, was carefully regulated so that the structures served as effective instruments of sacrificial rites, correct in all their parts.

According to an article by the “Mathematical Association of America,” fire-altar forms were intrinsically tied to specific aspirations for divine gifts. For instance, an individual aspiring for heavenly attainments was directed to construct a fire-altar in the likeness of a falcon. Similarly, someone desiring entry into the realm of Brahman was instructed to craft a fire-altar resembling a tortoise. Moreover, those seeking to vanquish present and future adversaries were advised to fashion a fire-altar in the configuration of a rhombus.

These prescribed fire-altar shapes symbolized profound spiritual aspirations and elucidated the intricate interplay between ritual architecture and desired outcomes in the sacrificial domain. [17] Moreover, these ancient Indian mathematical texts contain a significant geometric proposition, which became the Pythagorean Theorem. Additionally, the Vedic geometers encapsulated an approximation algorithm for the square root of two, accurate to five decimal places, and a method to approximate the squaring of the circle, employing only calibrated ropes. The ancient conundrum of squaring the circle held profound esoteric significance, as sacred geometers dedicated their lifetimes to attempting a geometrical amalgamation of the earthly and celestial realms.

The Sulbasutras also describe techniques to construct rectilinear shapes with areas equivalent to the summation, or difference, of other geometric figures. [18] In guiding the construction of three primary types of cosmic fire-altars, the Sulbasutras instruct that each one be encircled by a specific number of stones. “The circular altar symbolizing Earth was enveloped by 21 stones, the square altar representing the sky was encircled by 261 stones, and the space altar was encompassed by 78 stones”. [19]

Scholars often observe these three cosmic numbers within the architectural layouts of Hindu temples, including Angkor Wat, and these numerical patterns are generally regarded as having profound mathematical and cosmological significance. However, in Episode 1 of the History Fuzz podcast Professor Giulio Magli, an Astrophysicist and Archaeoastronomer at the Polytechnic University of Milan, attributed such patterns to a "selection effect," questioning the intentionality of such numerical occurrences in Hindu architecture.

Intentionality vs the Selection Effect

In 1996 researcher Eleanor Mannikka from the University of Louisiana published a paper in which she suggested the Khmer hat [cubit] was “standardized at approximately 0.43545 meters,” and she went so far as to say that it “served as the foundational module for the temple's architectural proportions.” [20] According to Mannikka, Khmer architects lifted data from calendars known as “chhankiteks,” and she proposed that the days in a solar year, “360, 365, or 366” were represented as building units. Furthermore, Mannikka also suggested lunar months (naksatras) were translated into lengths of 27, 28, or 29 building units, reflecting the number of days in a month.

Eleanor Mannikka concluded that “solar numbers are clearly present in the external axial dimensions of the topmost elevation of the central tower at Angkor Wat.” Measuring 189.00 cubits east to west, and 176.37 cubits north to south, the sum is 365.37 cubits, which the researcher concluded “is almost exactly the length of the solar year.” Furthermore, according to Mannikka, the distance between the western entrance to the Angkor complex, from the first step of the Naga balustrade walkway to the western doorway, is 354 meters [1,16 feet], ‘almost’ matching the number of days in a lunar year.

Contrary to these assertions, Dr. Gulio Magli told me that Dr. Mannikka’s interpretations were “numerical speculations” and he expressed the necessity for heightened skepticism when evaluating measurements of this nature. Professor Magli criticizes such numerological research, attributing Mannikka’s findings to the "selection effect," wherein researchers choose the data which best aligns with their preconceived notions. [21]

Rather than delving further into the intricacies of assessing intentionality with measurements, our focus will now shift to the mythological and then to the geographical inspirations that guided the rulers, architects, and builders of the Angkor Empire.

Journey to the Cosmic Centre

Scholar Daguan Zhou’s 2007 work, “A Record of Cambodia: The Land and Its People,” describes the central edifice at Angkor Wat as representing Mount Meru of Hindu mythology, with the walled enclosures mirroring the sacred mountain ranges encompassing Meru, and the surrounding square moat reflecting the Cosmic Sea. [22] How then, did this assembly of cosmic archetypes function?

Beginning at the entrance to the temple complex, at the west gate, the pilgrims first task was to traverse the Cosmic Sea. In Hindu mythology, at the suggestion of Vishnu, the devas and asuras used the serpent-king Vasuki as a churning rope in the primeval ocean in order to obtain amrita, the elixir of immortality. Pilgrims cross the Cosmic Sea walking along a stone causeway measuring 250 meters (820 ft) in length, and 12 meters (39 ft) in width, adorned with serpentine motifs. At the west gate, guarding the beginning point of this cosmic pilgrimage, is a seven-headed Naga - a mythological aquatic creature deeply-entrenched within Hindu and Khmer cosmogonic narratives.

In Stuart Fleming’s 1985 paper "Science Scope: The City of Angkor Wat: A Royal Observatory on Life?” the “Naga’ are described as an ancient reptilian race who played a central role in both Hindu and Khmer creation myths. Naga serpents are often depicted with an odd number of heads, symbolizing male energy and embodying the concept of the seven races within Naga society. This symbolism intricately correlates with the metaphysical constructs of the "seven heavens" and "the seven colours of the rainbow," reflecting the interconnectedness of cosmological and elemental principles within the context of Hindu and Khmer mythological paradigms. [23]

Hindu mythology recounts that under the rulership of ‘King Kaliya,’ who originally inhabited a vast otherworldly empire situated in the Pacific Ocean, the Naga migrated to India wherein his daughter married an Indian Brahmana named ‘Kaundinya,’ the mythological progenitor of the Cambodian people. Heinrich Zimmer’s 1981 book “Indische Mythen und Symbole” discusses a symbolic gesture that was made as a part of the wedding dowry, in which “Kaliya absorbed the waters that saturated the Cambodian landscape, exposing news farm lands for his daughter and son-in-law.” [24]

The Five Towers of Meru

Advancing over the Cosmic Sea and closer towards the central sanctum of the temple, pilgrims traversed through successive colossal enclosure walls which are believed to metaphorically evoke the sacred mountain ranges surrounding Mount Meru. Furthermore, this architectural arrangement symbolically embodies the hindrances that must be transcended along life’s path, on the spiritual odyssey towards enlightenment at the imaginary centre of one’s self. [25]

In Stencel and Gifford’s 1976 work “Astronomy and cosmology at Angkor Wat,” the researchers examined the sensory experiences and perceptual stimulations encountered by pilgrims at Angkor Wat, as they engaged with the cosmologically infused architectural elements. Stencel said the “monumental tower gateways, known as gopurams, serve as thresholds, progressively revealing more sacred domains, symbolizing the gradual detachment from the profane outer world as worshippers venture deeper into the spiritual sanctum”. [26]

Upon reaching the focal core of Angkor Wat, the central chamber, pilgrims passed through an encompassing square courtyard with four principal superstructures surrounding a colossal central tower symbolically emulating Mount Meru, the divine mountaintop abode of the gods in Hindu cosmology. Having transitioned from the human sphere into a more liminal realm, located directly beneath the highest tower is the central chamber, known as "God's Cave," denoting cosmic centrality and sacred transcendence, wherein mortals could commune with divine energies.

Unlike in other mediaeval faith traditions, in which the ruling clergy most often hold the keys to heaven, Hindus believed that the deity necessitated no intermediary agent. Therefore, God’s Cave, the central chamber in Angkor Wat, portrays an intimate spiritual node at the heart of the religious experience offered by the journey from the outside world. [28]

God’s Cave

The pinnacle of Hindu spiritual aspiration, unity with the divine, found its culmination where the horizontal axis traversed by the visitor, from the temple's west entrance to God’s Cave, meets the vertical axis of a temple. This point of geometric union symbolized the sacred Hindu trajectory from mountaintop to cave, and this juncture of axes was envisaged as the primal point of origin from which the entire cosmos emanated, at the very centre of the architects mandala design. [9]

Situated within God's Cave, beneath the mythical summit of Mount Meru, this darkened and confined space served as a spiritual convergence point, offering pilgrims a personal encounter with nirvana. Here, cosmological dualities melded into a cosmic singularity, thereby culminating the pilgrim’s expedition toward enlightenment.

This stone odyssey, which commences in the external realm at the west gate, traverses the Naga bridge and culminates within the sanctified enclave of God's Cave, is lined with elaborate wall carvings illustrating the pilgrim’s spiritual progression. Representing a deliberate perambulation through a mythic terrain, this cosmic-Khmer pilgrimage route encapsulated the fundamental archetypes of Khmer creation mythology.

Having outlined the mythological and cosmological underpinnings that define Angkor Wat, an examination of the profound connections between Angkor Wat and its surrounding topography offers an even more intimate comprehension of the interconnected cosmological narratives within the Khmer empire.

Khmer Astro-Architecture

In 2017, Professor Gulio Magli made a significant scholarly contribution through a seminal paper titled "Archaeoastronomy in the Khmer Heartland." Demonstrating how Angkor Wat boasts “meticulous measurements, precise orientations, and impeccable alignments,” Magli suggested that Angkor Wat served as a “near flawless manifestation of superior cosmic order”. [30]

Professor Giulio Magli applied Google Earth, Geographic Information System (GIS) data, and Stellarium, creating a reconstruction of the ancient Khmer celestial sphere. His research methodology adhered rigorously to the tenets of contemporary archaeoastronomy, systematically scrutinizing the interplay between astronomy, orientation, and topographical features while steering clear of “ambiguous or esoteric conjectures that had been posited by numerous scholars in the past”.

Magli noted that the majority of Angkorian temples exhibit “cardinal orientation within a range of 89 to 90 degrees east of north.” This means Khmer temples face the rising sun during both the vernal and autumnal equinoxes, in March and September, respectively, at the commencement of the sun's annual trajectory. According to Magli, this celestial event was of profound importance to the 12th-century Khmer populace whose societal fabric relied heavily on accurate lunar and solar calendars for religious and agricultural practices. [31]

In contrast to the common eastward orientation of Khmer temples, which like Christian churches, symbolized life, Angkor Wat's central tower faces west and is associated with themes of death and the afterlife, as described in Hindu and Buddhist cosmology. Furthermore, in their 1976 paper titled "Astronomy and Cosmology at Angkor Wat," researchers Stencel, Gifford, and Moron found that because Angkor Wat was orientated 270.5° west it caused those entering from the west gate to traverse the Cosmic Sea on the Naga causeway at a 90.5° angle. [32]

This half degree deviation from cardinality should be considered against the findings of the 2011 book, “Temples of Cambodia - The Heart of Angkor,” which describes the architects methods of orientation. By monitoring the shadows cast by a staff positioned at the conceptual nucleus of a nascent temple, over the course of a year, Khmer architects leveraged the ancient geometric expertise employed by Vedic rope-measuring specialists and derived accurate orientations with deviations “of less than 0.5 degrees”. [33] While the observed 0.5 - 1 degree variances north of the 90° orientation could be attributed to measurement inaccuracies, Professor Magli suggests they were “intentional rather than arbitrary.”

Magli noted a compelling pattern that emerged from his analysis of the azimuths of state temples such as Bakong, Phnom Bakheng, and Bayon, which mirror the orientation of Angkor Wat, but face east. All of these temples share a 0.5° deviation from the true east-west orientation, meaning they were not oriented to the spot on the astronomical horizon where the equinox sun emerged, which was the focus of astronomers following the passage of time, but the builders accounted for the sun's trajectory, post-sunrise.

Due to the steep sun trajectory at Angkor's latitude, this 0.5° deviation from a true east-west axis means that just after dawn on the equinoxes, when viewed from the west gate at Angkor Wat, the sun ascends above the central tower. Symbolically, a resplendent golden crown graces Mount Meru illuminating the highest point of the Cave of God at the centre of the temple, demonstrating a fusion of architecture and the divine.

The spectacle of the sun in the sky above the apex of Angkor Wat, in the moments after the equinox sunrise, was a materialization of the perceived connection between the earthly temple and the celestial realm of the gods. Symbolically synchronizing the heavens with the temples, the 0.5° deviation from a true east-west axis bolstered the spiritual experience of visitors, and it reveals that Angkor temples were not built as calendar-keeping tools, but they were aligned to reflect symbolic, artistic, or spiritual concepts. These temples were monuments of the sun cycle, rather than tools used to record it.

Sacred Khmer Latitudes

Not only did Khmer architects integrate profound religious symbolism, mythological principals, and cosmic order within the heavily-carved walls of Angkor Wat, but before a brick was laid teams of surveyors appraised the surrounding landscapes plotting the most significant natural features, and other temples, which could be associated with Angkor Wat through the symbolic orientation of its architectural features. As a discipline of archeoastronomy, “geodesy” finds its foundations in applied mathematics devoted to the study of Earth's dimensions, shape, and the positioning of various geographical points across its surface.

In Giulio Magli’s paper “Archaeoastronomy in the Khmer Heartland,” and in our recent podcast episode, he describes an abnormally long-distance east to west alignment uniting Angkor Wat with the Khan of Kompong Svay religious complex temple, located some 84.84 km [52.75 miles] to the east. Originally commissioned by King Suryavarman I during the 11th century, and greatly expanded by King Jayavarman VII in the 12th century, with an exterior perimeter of about 5 square km [1.93051 mi²], Khan of Kompong Svay has been described as “the largest Khmer enclosure ever built.”

Connected to Angkor by a royal road, Magli wrote that both religious sites “exhibit remarkable precision in their geographical positioning on the 13° 24' N latitude”. [34] He noted that the centers of both temples adhere to a common line of latitude “to an accuracy of “within 1 arc-second of a degree, constituting merely a few meters on the physical terrain.” Considering the formidable challenge posed by achieving such accuracy over 84.84 km [52.75 miles] Magli suggested the precision displayed in this long-distance alignment between Angkor Wat and Preah Khan at Kompong Svay, “demands interpretation grounded in cosmology and mythology, as it transcends functional astronomical purposes”.

Angkor Wat’s Solstice Alignment

Angkor Wat is situated at latitude 13° 26' N, so on both the June and December solstices the rising azimuth of the sun is 65.5° and 114.5°, respectively. Researchers Stencel, Gifford, and Moron explored what they deemed “the pivotal solstice alignment” that links Angkor Wat with Phnom Bok hill, approximately 14 kilometres [8.7 miles] to the northeast, and towering at an elevation of 220 meters [721.78 feet].

It was observed that people standing at the west gate of Angkor Wat, at the beginning of the pilgrimage route to the centre of the temple, on the morning of the June solstice, watched the sun “ascending from behind Phnom Bok hill.” The researchers suggested “potential intent” in this solstice alignment and they noted that Phnom Bok hill was perhaps symbolic of the mythical Mount Meru? [35]

In the late 9th century, King Yasovarman I orchestrated the relocation of the Angkorian capital from Hariharalaya to Yashodharapura, where eminent religious monuments like Angkor Wat were subsequently erected and integrated into earlier Khmer spiritual and political ideologies. In Stefano Vecchia’s 2007 paper “Khmer: history and treasures of an ancient civilization we learn that central to this spiritualized geographical domain stood the Phnom Bok hill-top temple, which predates Angkor Wat’s conception by King Suryavarman II in the mid-12th century by two and a half centuries. [36]

Atop Phnom Bok hill Yashovarman I built a Hindu temple-observatory bearing the same name, and having been aligned with the cardinal points of the compass this structure allowed for precise observations of the winter and summer solstice sun rise and settings against flat astronomical horizons in the east and west. In 1968, Historian George Coedes noted that a central aspect of Yashovarman I’s ideology was the ‘devaraja,’ or cult of the God King, which united kingship and the Hindu deity Shiva. [36] Phnom Bok temple featured a triple sanctuary dedicated to the Trimurti, a manifestation of the Hindu triad, comprising Brahma, Vishnu, and Shiva, illustrating the depth of cosmological symbolism enshrined within this temple-observatory’s architectural design. [37]

It becomes a possibility that two centuries later King Suryavarman II stood at his forbears Phnom Bok hill temple and watched the setting winter solstice sun, and precisely on that alignment he plotted the location for Angkor Wat. And in doing so, he also ensured that from the west gate at Angkor Wat the June solstice sun would be seen ascending from behind Phnom Bok hill. What’s more, further suggesting intentionality in this alignment, had Angkor Wat been positioned merely +/- 100 meters to the north or to the south, this solstice axis would not have transpired.

Interpreting this alignment symbolically, it should be considered that the divine essence of Shiva was worshiped in the form of the ‘linga’ (or lingam): a phallic symbol enshrined within mountain temples, such as the Phnom Bok temple which housed an enormous linga. In profound ceremonial rituals overseen by esteemed high priests, the divine essence of kingship was vested in new rulers through the linga.

In Devdutt Pattanaik’s 2006 work, “Shiva to Shankara: Decoding the phallic symbol,” we are told the safekeeping and veneration of the linga became intricately linked to “the security, prosperity, and divine favor bestowed upon the ruler and his kingdom.” Viewed from Angkor Wat on the June solstice sunrise, perhaps Phnom Bok hill itself epitomized a potent male linga being crowned by the rising sun? [38]

Dynastic Khmer Meridians

Jean Michele Delire’s 2009 book “Chronological inferences from a comparison between commentaries on different Śulbasūtras” explains that at the core of Khmer measurement methodologies, be they astronomical, cartographic, or architectural, the foundational step was to establish a precise east-west alignment. [39] Subsequently, an accurate north-south alignment, a prime meridian, denoting zero-degrees longitude was determined. Often measured from strategic vantage points such as harbours, capital cities, or highest peaks, prime meridians served as pivotal references for calculating time and distances, whether at sea, on land, or within the celestial expanse. [40]

Professor Magli has presented a compelling array of alignments representing ‘dynastic’ north-south meridians, with one prominent instance involving the Bakong temple [13°20′9.55″ N, 103°58′26.82″]. Built in the closing decades of the 9th century CE, Bakong stood as the inaugural Angkorian sandstone mountain temple, distinguished by its five stepped terraces, mirroring the topography reminiscent of the mythical Mount Meru.

About 1.8 km [1.118 miles] to the north of the Bakong temple is the 'Indrataka' - a massive baray (reservoir) built to receive diverted excess water from the flood season. Stella Kramrisch’s 1991 book “The Hindu Temple” explains that water was worshiped, cleansed, and fertilized before being irrigated into farmlands during the dry period which yielded a rice crop two or three times in one year. Not only did this ecological-engineering project strengthen the country's economy, but it released a large number of laborers for temple construction. [41] 

Professor Magli noted that the successor of Indravarman I (877-889 AD), Yasovarman I (889-910 AD), built the Lolei island temple [13°21′10″ N, 103°58′26″ E] “at the precise centre of the existing baray, directly upon the Bakong temple meridian.” The meridian was clearly a prominent symbolic-geographic feature, holding profound cosmological significance, where the divine geographic plan of one king was expanded upon by his predecessor. Hence the term, “dynastic” meridian. [42]

The 2015 paper, “Angkor Wat: an introduction,” published in the journal Antiquity, explains that in the latter part of the 9th century King Yasovarman I orchestrated a strategic relocation of his established capital, Hariharalaya, towards the northern expanse, culminating in the establishment of Yashodharapura. Yasovarman I embarked on the monumental task of erecting the expansive East Baray, the second-largest water reservoir in the Angkor region encompassing an extensive area measuring approximately 7.5 km [4.6608 miles] in length by 1.8 km [1.118 miles] in breadth, boasting a voluminous capacity of over 50 million cubic meters of water.

Only fifty years later Rajendravarman II commissioned the construction of the Pre Rup state temple, which he strategically positioned at a distance of 1.3 km [0.808 miles] to the south of the East Mebon temple, on precisely the same meridian. This meridian alignment binds geographic and dynastic concepts, similarly to the positioning of the Loiel Island Temple within the Indrataka, which was situated on the earlier Bakong temple meridian. [43]

These two principal meridians, identified by Professor Magli, effectively interlink the state temples with expansive barays, and they exemplify a clear lineage of ancestral heritage, wherein successive Khmer rulers expanded upon the north to south geographic blueprints of their predecessors.

Tomb of the Sun

In their 1976 work "Astronomy and Cosmology at Angkor Wat" professors Stencel, Gifford, and Moron noted that during the June solstice sunrise, at azimuth 65.5°, observers stationed at the western gate of Angkor Wat “bore witness to the spectacle of the sun ascending from behind the temple atop Phnom Bok hill,” approximately 14 kilometres to the northeast of Angkor Wat. [44]

Phnom Bok hill-top temple was built during the reign of Yasovarman I in the early 10th century and it was one of the four elevated temples commissioned during his rule, alongside Phnom Bakheng, Phnom Krom, and Phnom Dei. However, Professor Magli argues Stencel, Gifford, and Moron’s assertions, pointing out that Phnom Bok hill is about 220 meters (721.78 feet) high, and not particularly prominent from Angkor Wat. He wrote that for this alignment to have been intentional, “one would have to assume that the entire siting of Angkor Wat as a whole was largely governed by a desire to create this alignment, something for which there is no cultural basis whatsoever.” [45] However, there is a perhaps a missing element, which might give this solstice alignment the cultural and dynastic significance that seems to be lacking.

During Yasovarman I's reign the sacred topography of his kingdom was extended eastwards to incorporate Phnom Bok and Phnom Dei hills, and while his Bakong temple was being completed he ordered the building of temples on top of both rises. These two elevated locations form a natural north-south axis and according to "Cambodian Architecture, Eight to Thirteenth Century" (2001), Yasovarman I “personally oversaw the construction of temples atop these two hills.” Might Yasovarman I have deliberately positioned these two temples to form a meridian? Most likely for symbolic, but perhaps for astronomical purposes? [46]

Testing this hypothesis, Phnom Bok temple is situated on longitude 103°58′55″ E and Phnom Dei temple is positioned at longitude 103°59′1″ E. These coordinates reveal that the north-to-south alignment between the two hilltop temples maintains a remarkable level of accuracy across a span of about 14.5 kilometres, with a mere variance of 6.000012 arc seconds, or less than 0.69 meters, from a common meridian. This level of precision suggests deliberation in the positioning of the two temples, rather than the proposed alignment being coincidence/chance.

Accepting that Phnom Bok and Phnom Dei hill temples were deliberately built to manifest a north to south meridian, it might be the case that the 10th century King Yasovarman I established this longitudinal line to define the eastern limits of his kingdom, with his Bakong temple at the centre marking the first state prime meridian.

Supporting the idea that Yasovarman I’s 10th century hilltop temple meridian was indeed an established Khmer alignment, it appears that the12th century King Suryavarman II, while he was expanding his kingdom, extrapolated a 245.6° azimuth [December solstice sunset] from Phnom Bok hill to locate Angkor Wat. Conversely, this solstice axis also assured viewers at Angkor Wat saw the sun rising from behind the hill on the morning of the June solstice.

Having established a “dynastic heritage” for the locating of Angkor Wat, in which one ruler used a previous’ meridian to located his main temple, the “cultural” basis for the alignment, which Professor Magli requires, is perhaps found in the associations between the winter solstice and death of light. One cannot overlook the fact that Angkor Wat was designed to serve as King Suryavarman II’s tomb. [47] Thus, standing on Phnom Bok hill, or Mount Meru, the dying winter solstice sun was seen sinking into Angkor Wat, serving symbolically as a tomb of the sun.

Mirroring Ancient Meridians

Further exploring the plausibility of the proposed Phnom Bok - Phnom Dei hilltop temple meridian, a noteworthy observation comes from the acknowledgment that Phnom Bok hill did indeed function as a foresight for observing the summer solstice sunrise from Angkor Wat. At the north terminus of this possible meridian, Yasovarman I built Phnom Dei Hill temple approximately 14.5 kilometres to the north of Phnom Bok Hill, and the question arrises, might Phnom Dei Hill also have been used as a foresight for observing the summer solstice sunrise, from a currently unidentified temple to the north of Angkor Wat?

Exploring this notion, a 245.6° winter solstice setting azimuth was drawn southwest from Phnom Dei Hill temple. This alignment, as was predicted, identifies Prasat Kamboch temple, also built by King Suryavarman II in the 12th century. Little is known about the nature of this temple, that encompasses about 350 square meters, but the remains of a small brick building, pedestals, blocks and colonette are still present. The temple sits within a moat, with a 200-meter-long baray to the east, therefore, on the morning of the summer solstice observers at the Prasat Kamboch temple watched the chief star rising behind Phnom Dei hill at 65.5°. And, in reverse, observers standing at Phnom Dei hilltop temple on the winter solstice watched the setting sun sinking into Prasat Kamboch temple in the south west. [48]

Lending further support to the suspected intentionality of the positioning of Prasat Kamboch temple by King Suryavarman II as an observing platform to watch the June solstice sun rising behind Phnom Dei hill, he could have chosen any longitude in the kingdom on the 245.6° winter solstice sunset azimuth from Phnom Dei hilltop temple, to build Prasat Kamboch temple. However, the temple was centred directly upon Angkor Wat’s meridian.

Over approximately 14.5 kilometres the longitudinal centres of Angkor Wat “103.8670°” and Prasat Kamboch “103.86612°” have a 0.2966°, or 43 meters variance, suggesting Suryavarman II attempted to reflect the length of Yasovarman I's Phnom Bok hill meridian in the building of these two temples. Symbolically, on the summer solstice, the Angkor Wat meridian of Suryavarman II was astronomically and geographically united with his predecessor Yasovarman I's 10th-century hill meridian. Figure 4.0 illustrates the proposed Phnom Bok - Phnom Dei hilltop temple meridian and the 12th century Angkor Wat to Prasat Kamboch temple meridian.

Perhaps groups of observers were stationed at both temples to witness the summer solstice sun rising from behind Yasovarman I’s two raised hilltop temples, which were crowned, similarly to the way in which Angkor Wat is crowned by the rising equinox sun.

Conclusions

It appears that in the 12th century when King Suryavarman II was choosing locations for Angkor Wat and Prasat Kamboch, he plotted two 65.6°-245.6° solstice alignments from the Phnom Bok hill and Phnom Dei hill temples, respectively, that were both built by King Yasovarman I, his 10th-century predecessor. If indeed the 12th-century King Jayavarman VII deliberately positioned Angkor Wat and Prasat Kamboch temples so that the rising summer solstice sun was seen ascending from behind his ancestor Yasovarman I’s hill temples, this shows a spectacular reverence for an antecedents previous meridian and demonstrates the fusion and expansion of sacred geographical templates.

If this was the case, not only did Jayavarman VII glorify two of his ancestors temples, which were crowned by the sun on the June solstice, but he also laid out a meridian with a length equal to that of his predecessor, providing both dynastic and cultural associations.

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