The Dalai Lama espouses the spiritual teaching of Je Tsongkhapa (1357 – 1419), a philosopher who founded the Gelug version of Buddhism. Je Tsongkhapa established his first monastery in Lhasa in 1409. Soon after, the first Dalai Lamas took over the running of his monastery and others that had built up. In fact, this branch of Buddhism is a revivalist movement, bringing back the ideas of Atiśa, a Bengali Buddhist who taught in the eleventh century. Much focus is placed on ethics and monastic discipline within the Gelug school. The Guhyasamāja tantra is another central aspect of the Dalai Lama's teaching, which focusses on 'oneness' whether that is in study or in meditation.