For centuries, tea travelled on the backs of donkeys, horses and yaks. There were a number of tea routes. They started at the Chinese provinces that produced compressed teas (Yunnan, Sichuan, etc.) and led to Tibet. In those days, tea was traded for salt or horses.
To perpetuate this tradition today, some people hold re-enactments, and you can watch hundreds of animals file past, carrying cakes of tea.