Ganden Monastery. Prayer flags mark the limit of pilgrims' excursions into the hills around Ganden. They are usually strung around sacred places to purify the air and pacify the gods, and their fluttering is believed to release their written prayers into the heavens. The colours too are symbolic of the elements. Ganden was the first Gelugpa school monastery. Founded in 1409 by Tsongkhapa and with a monastic population that reached 3000, it was severely damaged during the Cultural Revolution.