In a method perfected over centuries, the Khasi bridge builders weave aerial roots onto a bamboo or another wooden scaffolding, wheedle them across the river and finally implant them on the opposite bank. Over time, the roots shorten, thicken and produce offshoots called daughter roots, which are also trained over the river. The builders intertwine these roots with one another or with branches and trunks of the same or another fig tree. They merge by a process called anastomosis – where branching systems like leaf vessels, tendrils and aerial roots naturally fuse together – and weave into a dense frame-like structure. Sometimes, the Khasi builders use stones to cover the gaps in root structures. This network of roots matures over time to bear loads; some bridges can hold up to 50 people at once.