Ta Keo is sometimes spelt Takeo or Ta Kaeo or called Prasat Keo. The modern name Ta Keo, pronounced "Takaeoo", means "tower of crystal". In contemporary inscriptions it is mentioned as Hemagiri or Hemasringagiri, meaning "mountain with golden peaks".
Ta Keo was the state temple of Jayavarman V (968-1001). He began building it about 975, when he became adult and started to rule independently after a period of government by other court officials. Like former state temples (Bakong in Roluos, Bakheng in Angkor, Prasat Prang at Prasat Thom in Koh Ker, and Pre Rup in Angkor), it was dedicated to Shiva and enshrined a Lingam as symbol of divine and royal power and was built as a temple-mountain with Prasat Towers on top of a step pyramid. Unlike temple-mountains of the preceding kings, Ta Keo was not built in the centre or inside the new king's city called Jayendranagari (not yet verified), but sited due north, close to the west bank of Angkor's East Baray, which was its main reservoir at that point in time. There was a causeway connecting the east entrance of Ta Keo with the former Baray in half a kilometre distance.
Ta Keo is surrounded by a moat, which is now dried up, except after heavy rainfall. The outer temple wall, forming a 122 metres long and 106 metres wide rectangle, is not built on ground level, as usual, but at the edge of the first tier of the pyramid, which leaves the impression of a fortress. Inscription on the pilasters at the east gate record the temples's foundation.
Ta Keo's pyramidal structure is 21.5 m high. Its less steep eastern stairway still has a 55 degree gradient and is not easy to climb. The typical step pyramid Ta Keo, all in all, is the the most proportioned of the Khmer state temples preceding the Angkor Wat.
The majestic Ta Keo is the first temple constructed entirely of sandstone, enormous blocks were cut at the quarries of Phnom Kulen in 30 kilometres distance. Their accuracy is all the more astonishing as this kind of greenish grey sandstone, called feldspathic wacke or greywacke, is very hard to carve.
Furthermore, Ta Keo is the first Angkor temple with a straight gallery instead of a series of rectangular structures. Interestingly the brick-roofed gallery of Ta Keo had no doors, it appears to be purely decorative. Galleries became a main characteristic of later Khmer temples, e.g. the state temples Baphuon, Angkor Wat, and Bayon in Angkor Thom. So Ta Keo introduces the combination of three classical characteristics of imperial Khmer architecture: rising levels, enclosures with galleries, and five Prasat towers arranged in a quincunx.
At the foot of the eastern staircase there is a statue of a kneeling Nandi bull, Shiva's mount. Ta Keo's upper platform is square and almost entirely occupied by this quincunx of Prasats, similar to Pre Rup built by Jayavarman's father Rajendravarman. The central tower reaches a total height of 45 metres above ground level. All five towers are on cruciform bases and, as an innovation, open to all four cardinal points by projecting vestibules. So in this case there are no false or blind doors at the outer Prasat walls (they are found only at the corners of the central tower).
Ta Keo is plainly decorated, only on the east face there are some damaged stone carvings of floral patterns. The complete lack of lintel carvings is surprising. The usual explanation for this peculiaritiy is that Ta Keo remained unfinished. Yogishvara Pandita, a high priest who became minister of Suryavarman I and was in charge of Ta Keo, but felt himself unworthy of occupying the upper levels of the temple, records in inscriptions that a lightning strike hit the still unfinished building, so the works stopped because of this evil omen. But still there are unanswered questions. Jayavarman V reigned many decades, and this state temple, unlike some others of his predecessors, was not abandoned after his death. Quite the reverse, works at Ta Keo were continued by Suryavarman I (1002-1050), whose rule also was stable and lasted a long time.
The afternoon is the better time for viewing the pyramid as a whole, from the Small Circuit road. The morning is better for seeing the main entrance and for climbing to the top. The Angkor ticket is obligatory for access to the elevated compound of Ta Keo.