Isana is one of Shiva's names, and the king who founded this capital had already built it into his own: Isanavarman, protected by Isana. He ruled from roughly 616 to 637 over the polity Chinese sources call Chenla, and he established his city here around 618. Almost immediately he worked the diplomatic channels - an embassy reached the Sui court in 616 or 617, early enough that the historians compiling the Book of Sui had reasonably fresh testimony to draw on. One inscription at the site carries a startlingly precise date, 13 September 627, which is an unusual point of light for a period this dimly lit. Another from his reign calls him king of kings, ruler over Suvarnabhumi, the golden land of Indian tradition. Kings claimed a great deal in stone. What a boast like that reliably tells us is not how far his writ ran, but how far he wanted it read.

Here is the awkward thing about every sentence written on this subject. Chenla - Zhenla in Mandarin - appears in Chinese dynastic records and nowhere in Old Khmer. No local inscription uses it. The same is true of Funan, the older Mekong polity that Chenla is said to have absorbed. Both are filing labels applied from outside, by a court that preferred its tributaries arranged tidily on a page.

Michael Vickery pressed the point hardest, arguing that before 802 there was no single great state in Cambodia at all, only a shifting field of principalities that Chinese scribes bundled under one heading. The later division into Land Chenla and Water Chenla after 707 he dismissed as an artifact of that same bookkeeping. So Isanapura is real, its moats and inscriptions are real, and the kingdom it supposedly capitalised is a category inherited from somebody else's archive.

What stands above ground here is temple. What lies below it is city, and only recently has anyone been able to make out the shape. LiDAR flown over the site resolved a four-by-four grid - planned, deliberate, not an organic sprawl. A moat roughly two kilometres long wraps the western settlement on three sides, and the fourth is closed by the seasonal O Krue Ke. Running east from the centre of the grid toward the temple groups is a linear feature twenty metres across, water of some kind, canal or moat.

At the grid's heart, excavation found the terrace: laterite and brick, seventy metres north to south by fifteen east to west, its retaining walls still standing 2.1 metres high. Square brick pads sit at metre-and-a-half intervals on all four sides, spacing that would suit timber posts, though no timber survived to settle the question. Radiocarbon from surrounding structures brackets Isanavarman I and his successor Bhavavarman II. Other charcoal samples run from the fifth century to the fifteenth. Whatever happened to the dynasty, people did not simply walk away from the place.

European identification of the capital came slowly. A first study was made in 1912; then in 1927 Henri Parmentier surveyed it for the Ecole francaise d'Extreme-Orient and became the first to treat the ruins as a city rather than a scatter of shrines. Twenty-three inscriptions have been recovered in the century since. That is not much to reconstruct a royal capital from, and the thinness leaves room for genuine disagreement - Claude Jacques argued that this site was not Isanapura at all but Bhavapura, another name known from the epigraphy. Most scholars have not followed him there. The dispute is still worth knowing, because it shows how lightly the famous names sit on the actual ground.

The last king of consequence here was Jayavarman I, who ruled roughly from 657 to 681 and whose inscriptions show a reach well beyond the Stung Sen basin. His death broke it apart. The eighth century in Cambodia is a fog of small competing centres, and the fog does not lift until 802, when Jayavarman II declared himself universal monarch and settled at Hariharalaya on the plain that would become Angkor.

Isanapura lies 176 kilometres east of Angkor. The distance in time is a century and a half of fragmentation, which is why the two rarely appear in the same paragraph. But the carved lintels made here, the brick towers, the habit of setting a sanctuary inside a walled enclosure - those travelled. Angkor did not invent Khmer architecture. It inherited it, from a capital on the Stung Sen that most visitors to Cambodia have never heard of.