Nobody knows who built Beng Mealea. No founding inscription survives, no royal name attaches to it, and the entire chronology rests on how the thing looks. What it looks like is Angkor Wat. The blind doors, the lintels, the pediments, the cruciform cloisters, the magnificent five-headed nagas rearing off the terraces - all of it belongs to the Angkor Wat style, which puts the temple in the early 12th century and points at the reign of Suryavarman II, who built Angkor Wat itself. The outer gallery measures 181 by 152 metres, and the floor plan is close enough to Angkor Wat's that the temple is commonly described as a forerunner or blueprint for it. Whether the builders were rehearsing or simply repeating a design they had already perfected is a question the stones refuse to settle.

The name means Lotus Pond, and it is not decorative. Beng Mealea was the centre of a town, ringed by a moat 1,025 metres by 875 and fully 45 metres wide - a rectangle of open water big enough to see from a long way off, in a landscape where controlling water was the whole basis of power. It was founded as a Hindu temple, though some of its carvings show Buddhist motifs, a doubling common enough across late Angkorian Cambodia. Much of the best sculpture is now horizontal. Female deities look out from walls that have tilted off plumb; one fallen lintel lies where it landed, still showing the Churning of the Sea of Milk, the gods and demons hauling on their serpent rope while the world is made. You come around a heap of rubble and there it is, at your feet, face up to the sky.

Beng Mealea's ruin is old, but its inaccessibility was modern and man-made. Cambodia's wars left this stretch of country mined, and mined ground does not permit archaeology, tourism or even casual trespass. The temple sat behind that barrier for years - not lost, simply forbidden, a place local people knew perfectly well and could not safely enter. It took deminers working the ground metre by metre to change that. Around 2003 the Cambodian Mine Action Centre and the HALO Trust finished clearing the site, and the temple opened to visitors. The clearance was slow, dangerous, largely unglamorous work carried out by Cambodians on Cambodian soil, and it is the single reason anyone can stand inside these galleries today.

Being unguarded and unrestored also made Beng Mealea vulnerable in a second way. The site has suffered serious damage from antiquities theft - heads removed from bodies, reliefs chiselled out of their settings, structures further destabilised in the process of extracting a saleable fragment. The economics are brutally lopsided. A carving that fetches a large sum in a distant gallery may pass through the hands of someone in a nearby village for a tiny fraction of it, and the loss to the site is permanent regardless of who profited. Cambodia's recent success in recovering trafficked Khmer sculpture has changed the calculus somewhat. But a statue can come home to a museum; a pediment cut out of a standing wall cannot really be put back, and Beng Mealea carries those subtractions in plain view.

Beng Mealea was documented early - a map survives from a drawing by the French officer and scholar Leon de Beylie, who died in 1910 - and it has been visited, studied and photographed ever since without ever being reassembled. The site was added to Cambodia's UNESCO World Heritage Tentative List in the cultural category on 27 March 2020, having first been proclaimed on 1 December 1992. Restoration would tidy it and would also erase the thing it uniquely offers: an unedited demonstration of what a thousand years of monsoon, seed and root actually do to sandstone. The figs are not a picturesque accident. They are the process, still running. Walking the plank path through the collapse, with the light coming down in shafts through the canopy and the moss growing on carved apsaras, you get a version of Angkor that the nineteenth-century explorers described and that almost nowhere else still delivers.