Rivalling even the great pyramids of Giza, the gargantuan structure of the Abhayagiri Stupa in Anuradhapura goes back to the 1st century BC. The origins of the stupa are associated during the reign of King Valagamba, when he was initially driven out by the Dravidian invaders. During the time he was fleeing away from the kingdom, a Jain monk insulted him, which made him promise to build a temple in which the monk stood when he regained the kingdom, and that is exactly what the king did after 14 years of exile.
What makes this unique monument a major site in the ancient city is the fact that the king built it as a major pilgrimage site for the three sects of Buddhism, namely Mahayana, Theravada and Vajrayana. Although having an intriguing backstory, the stupa was destroyed and neglected due to the eventual invasion of the Cholas. The stupa that can be witnessed today is a heavily restored complex made with clay bricks, and was made to resemble the original structure.
The complex is also known to possess ancient relics that belonged to the Lord Buddha, along with the oldest known moonstone carvings (reminiscent to that of an elaborate welcome mat) in the world.