Each monastery had its own estates, and all the people farming on these estates paid taxes in money and goods. One of the main tasks of the stewards was to increase this income; for instance, by lending grain back to the peasants at high interest rates, or selling goods at market. Before the destruction of the monasteries in the 1960s, they owned as much as half of Tibet’s farmland.
The description however is referring to the 15th century. Another interesting part of the book concerns how, during Tibet’s “Golden Age,” the Tibetans tried to impose their language and culture on the neighboring regions of China, and with some success.
That is all from Sam Van Schaik, Tibet: A History.