The Mahaviharavasin was a conservative sub-sect or fraternity of the Theravada tradition in Sri Lanka. The fraternity resisted attempts to introduce  Mahayana influences and maintained strict adherence to the Pali Canon which it was responsible for committing to writing in seventeen BCE.

Around 247 BCE King Asoka sent a mission to Sri Lanka where the Sri Lankan king, Devanampiyatissa established a monastery called the Mahavihara at his capital, Anuradhapura. The Mahavihara monks enjoyed royal patronage which contributed to rivalry between developing monasteries. In the last decades before the beginning of the common era a later king Vattagamani gave a new vihara, at Abhayagiri, to an individual monk which resulted in his expulsion from the Mahaviharavasins because the personal gift infringed the monastic rule. The favoured monk's disciples followed him and the Abhayagiri fraternity was formed. The Abhayagiri monks were later influenced by Mahayana ideas and rivalry continued between the two fraternities.
     In the fourth century a new move to introduce Mahayana ideas to Mahaviharavasin monks resulted in the formation of a further fraternity at the Jetavana monastery. At this time the Mahavihara monastery was destroyed but later rebuilt under royal patronage. The  Mahaviharavasins continued to be influential in Sri Lanka, maintaining their own conservative doctrinal position. Buddhaghosa, the Indian monk who travelled to Sri Lanka in the fifth century and was responsible for compiling much of the Theravadin commentarial literature was associated with this fraternity. The three fraternities vied for royal patronage, and therefore supremacy, over several centuries until in the twelfth century King Parakkama Bahu I abolished the Abhayagiri and Jetavana ordination lineages. From this time Theravada Buddhism has followed  Mahavihara orthodoxy.

See  Theravada.

No official figures.

The Great Monastery at Anuradhapura in Sri Lanka.