Abhayagiri Vihāra was a major monastery site of Mahayana, Theravada and Vajrayana Buddhism that was situated in Anuradhapura, Sri Lanka. It is one of the most extensive ruins in the world and one of the most sacred Buddhist pilgrimage cities in the nation. Historically it was a great monastic centre as well as a royal capital, with magnificent monasteries rising to many stories, roofed with gilt bronze or tiles of burnt clay glazed in brilliant colors. To the north of the city, encircled by great walls and containing elaborate bathing ponds, carved balustrades and moonstones, stood "Abhayagiri", one of seventeen such religious units in Anuradhapura and the largest of its five major viharas. One of the focal points of the complex is an ancient stupa, the Abhayagiri Dagaba. Surrounding the humped dagaba, Abhayagiri Vihara was a seat of the Northern Monastery, or Uttara Vihara and the original custodian of the Tooth relic in the island.
The term "Abhayagiri Vihara" means not only a complex of monastic buildings, but also a fraternity of Buddhist monks, or Sangha, which maintains its own historical records, traditions and way of life. Founded in the 2nd century BC, it had grown into an international institution by the 1st century AD, attracting scholars from all over the world and encompassing all shades of Buddhist philosophy. Its influence can be traced to other parts of the world, through branches established elsewhere. Thus, the Abhayagiri Vihara developed as a great institution vis‑a‑vis the Mahavihara and the Jetavana Buddhist monastic sects in the ancient Sri Lankan capital of Anuradhapura.