The Mahàvihàra, or Great Monastery, was the monastery founded by Mahinda, who introduced Buddhism into Sri Lanka in the 2nd century BCE.
The monastery was situated just beyond the southern wall of Anuràdhapura, the ancient capital of Sri Lanka. When the Chinese pilgrim Fa Hien visited Sri Lanka in the 5th century, there were 1500 monks in the Mahàvihàra. For many centuries it was a centre of religion, culture and learning. The interpretation of the Pali Tipitaka called Theravada Buddhism evolved in the Mahàvihàra from the 1st century BCE onwards. In later centuries, monks of the Mahàvihàra tradition established Theravàda Buddhism in Burma and Thailand from where it later spread to Cambodia and Laos. The Mahàvihàra was abandoned after the capital of Sri Lanka was shifted to Polonnaruva in the 9th century.
History of Buddhism in Ceylon, Walpola Rahula, 1956.