According to the Sri Lankan chronicle tradition, the emperor Ashoka sent a Buddhist mission to Sri Lanka in the third century BCE, traditionally led by his son, the monk Mahinda, who converted the reigning king, Devanampiya Tissa, at Mihintale near Anuradhapura. Ashoka's daughter, the nun Sanghamitta, is said to have followed with a cutting from the original Bodhi Tree at Bodh Gaya, the tree under which the Buddha attained awakening, and the sapling was planted at Anuradhapura with royal ceremony. The tree standing there today is maintained as a direct, unbroken descendant of that planting, tended continuously through more than two thousand years of the island's changing fortunes, which makes it, by the documentary record kept around it, the oldest known tree of human planting still growing at its original site anywhere in the world, a distinction of particular weight given that the original tree at Bodh Gaya itself has had to be replanted from cuttings more than once after damage and destruction over the centuries.
Devanampiya Tissa's conversion made Anuradhapura the capital of a Buddhist kingdom, and the Mahavihara monastery founded there became the center of the Theravada textual tradition that Sri Lanka would later transmit, in its Pali form, across mainland Southeast Asia. The city's skyline came to be dominated by enormous stupas, among them the Ruwanwelisaya, built under King Dutugemunu in the second century BCE and still, at nearly one hundred meters, one of the tallest ancient monuments in South Asia.