Protected site
Tim Curtis, chief of Unesco's culture department in Bangkok, gave me a picture of what the city was like. "It was very cosmopolitan, with all the overseas traders. The canals used to move around the city were always busy. In the 17th Century it was one of the world's largest cities, as big as Paris," he says.
The temples, he explains, were built both to enhance the prestige of kings but also to accumulate merit for the entire community.
What's left of the old kingdom is preserved as a Unesco World Heritage Site, but the UN body is engaged in constant negotiation with Thai authorities to improve the ruins.
"What we'd like to see is a greater sense of connection between the old and the modern city", says Tim Curtis, "Venice, another water city, is a good example".
The pressures of modern development have caused damage to historic sites: vibrations from traffic and inappropriate construction. Much of Ayutthaya resembles any other Thai provincial city - rows of unattractive, concrete shop-houses, built to a budget.
But the economic transformation of Ayutthaya has also raised living standards.
We went out at dawn to a major intersection, to watch thousands of uniformed workers lining up to take buses to industrial estates just outside the city. There are now more than 2,000 factories in Ayutthaya, employing around 200,000 people.