The restoration of Sinhalese power began in 1070 when Vijayabāhu I, a prince of the royal blood, rallied the forces of Ruhuṇa and, after years of guerrilla warfare, finally expelled the Cholas from the island. He established a new capital at Polonnaruwa, the very city the invaders had built, and set about the work of reconstruction. But the political unity of Lanka remained very fragile, and it was not until the mid-12th century that a monarch of sufficient vision and strength arose to complete the task. Parākramabāhu I, through a series of courageous campaigns, brought the entire island under his sole authority for the first time in nearly two centuries. Having unified the secular realm, he then turned his attention to the condition of the Saṅgha, which he found fractured, demoralized, and in desperate need of reform. The stage was now set for one of the most significant religious councils in Theravāda history.
In 1164 or 1165, Parākramabāhu convened a great council of the monastic community, summoning the most respected elders from across the island. Chief among them was Mahākassapa Thera of Udumbaragiri, a forest-dwelling bhikkhu renowned for his strict adherence to the Vinaya and deep learning. The King, acting in the tradition of great Buddhist emperors like Asoka, placed his royal authority at the service of the elder’s spiritual judgment. The council’s decision was radical: the three fraternities were to be dissolved, and their members merged into a single, unified Saṅgha under the sole authority of the Mahāvihāra. A comprehensive purification was then carried out. Bhikkhus found to be living in violation of the Vinaya—those who were married, who engaged in trade, who refused to follow the rules—were summarily defrocked. Those deemed worthy were permitted to remain and were, in many cases, re-ordained to ensure the absolute purity of the lineage.
The reforms were codified in a detailed inscription carved into rock at Gal Vihāra, which survives to this day, and which is a very important Buddhist historical monument. This consequential edict functioned as a kind of constitution for the Saṅgha going forward, prescribing the duties of bhikkhus in detail: their obligations to study the scriptures, to practice meditation, to maintain proper deportment, and to avoid association with the wrong people and the distractions of worldly life. It also established a clear hierarchy of authority and a system of penalties for transgressions. The Polonnaruwa reform was a well-needed purge, which helped reset the direction of the monastic order.