In 1578 Altan Khan, a Mongol nobleman and military leader with ambitions to unite the Mongols and to emulate the career of Chinggis Khan, invited the head of the rising Yellow Sect of Tibetan Buddhism. Since then Yellow Sect Buddhism spread throughout Mongolia. Tibetan styled monasteries were built across Mongolia, often sited at the juncture of trade and migration routes or at summer pastures. Traditionally, monasteries were centers both of learning and of power. In the per-revolutionary period, Mongolia was ruled by a series of Living Buddhas called Javzandamba. It is estimated Mongolia had 100 000 monks in 1921; one third of the male population. In the 1930s, this intellectual power became the focus of a ruthless series of purges. Today, Mongolia is once again embracing its Buddhist heritage. Monasteries are being restored and are once again crowded with worshipers.