You watched the trooping army’s fluttering banners; horses draped in gold; ministers with red umbrellas; and behind them all, the king standing on an elephant, its tusks shining with gold.

It was 1297 and your diplomatic trip to Angkor was over, Zhou Daguan, but you were reluctant to leave the thriving city of seven-hundred-and-fifty thousand people at the heart of the Khmer Empire.

It was so beautifully ordered, how could you describe it to your Emperor? Angkor Wat was the most palatial temple you had ever seen. It evoked Mount Meru, font of the cosmos, with its five gilded towers rising like peaks, and its immense artificial lakes symbolising the oceans. Its sacred reservoirs were practical too, storing monsoon rains to guarantee harvests; they were the source of the city’s six centuries of success.

But the system had become too ambitious, too reliant on a stable climate.

When the first drought hit, the empire lost its outlying lands. When the next drought hit, the city failed. Angkor fell to invaders. They tried to use its finely-balanced infrastructure, but it was beyond repair.

The largest city in the pre-industrial world was abandoned, reclaimed by the jungle, and the wonders of the Khmer Empire were forgotten by all.

Angkor