the country for nearly 1,400 years. Ancient Sri Lankans excelled at building certain types of structures such as tanks, dagobas and palaces. Society underwent a major transformation during the reign of Devanampiya Tissa, with the arrival of Buddhism from India. In 250 BCE, Mahinda, a bhikkhu and the son of the Mauryan Emperor Ashoka arrived in Mihintale carrying the message of Buddhism. His mission won over the monarch, who embraced the faith and propagated it throughout the Sinhalese population. Succeeding kingdoms of Sri Lanka would maintain many Buddhist schools and monasteries and support the propagation of Buddhism into other countries in Southeast Asia. Sri Lankan Bhikkhus studied in India's famous ancient Buddhist University of Nalanda, which was destroyed by Bakhtiyar Khilji. It is probable that many of the scriptures from Nalanda are preserved in Sri Lanka's many monasteries and that the written form of the Tripiṭaka, including Sinhalese Buddhist literature, were part of the University of Nalanda. In 245 BCE, bhikkhuni Sanghamitta arrived with the Jaya Sri Maha Bodhi tree, which is considered to be a sapling from the historical Bodhi Tree under which Gautama Buddha became enlightened. It is considered the oldest human-planted tree (with a continuous historical record) in the world. (Bodhivamsa) Sri Lanka experienced the first of many foreign invasions during the reign of Suratissa, who was defeated by two horse traders named Sena and Guttika from South India. The next invasion came immediately in 205 BCE by a Chola named Elara, who overthrew Asela and ruled the country for 44 years. Dutugamunu, the eldest son of the southern regional sub-king, Kavan Tissa, defeated Elara in the Battle of Vijithapura. During its two and a half millennia of existence, the Sinhala Kingdom was invaded at least eight times by neighbouring South Indian dynasties such as the Chola, Pandya, Chera, and Pallava. There also were incursions by the kingdoms of Kalinga (modern Odisha) and from the Malay Peninsula as well. The Fourth Buddhist Council of Theravada Buddhism was held at the Anuradhapura Maha Viharaya in Sri Lanka under the patronage of Valagamba of Anuradhapura in 25 BCE. The council was held in response to a year in which the harvests in Sri Lanka were particularly poor and many Buddhist monks subsequently died of starvation. Because the Pāli Canon was at that time oral literature maintained in several recensions by dhammabhāṇakas (dharma reciters), the surviving monks recognised the danger