Ordinary bridges would rot under the relentless drenching of the monsoon. What's clever about these root bridges is they get stronger as they get older.

 

So wide. I mean, a whole village could get through here.

 

Surprisingly, the intensity of the monsoon rain is all down to a basic property of water. Compared to other substances, water takes a lot of energy to heat up. So the land and the ocean react very differently to the rising temperatures of early summer. During these months, India's land surface heats up much more than the surrounding Indian ocean. The high temperature reduces the density of the air, creating low pressure. That sucks moist ocean air onto the land, which brings rain. It’s because the whole system is driven by the sun's heat that the rains come in the summer. But it also means that the monsoon only lasts for three months of the year. For the rest of the time, there’s virtually no rain.

 

Adapting to the water cycle has made the difference between success and failure for many civilizations. But there was another strategy that also brought success. And that was to take control of the water cycle. There was one early civilization above all others that took control of the planet's most dramatically changing source of water. They mastered the monsoon. They were the Khmers, and from the nineth century, they dominated the area we now know as Cambodia.