Devanampiya Tissa, second son of Mutasiva , succeeded the throne around 247BCE, about 236 years after the accession of Vijaya. He ruled Anuradhapura for forty years. He was a friend of Asoka even before he became king but the 2 had not met each other. Asoka introduced proper form of coronation for the new King of SL and provided all the elaborate requisites. The honorific title of “Devanampiya” [Beloved of the Gods] was conferred by Asoka onto King Devanimpiya Tissa. The 1st thing he did when he became king was to send envoys to Asoka, bearing costly gifts.
The envoys returned and brought among other things this message from Asoka:“I have taken refuge in the Buddha, his Dhamma and His Sangha, I have declared myself a lay-disciple in the religion of the Sakya son. Seek then, O best of men, refuge in these best of gems, converting your mind with believing heart.” In the year 247 BCE, Ven Mahinda & his companions arrived in Sri Lanka on full-moon day of the month of Jettha (A month after the Vesak month). This day was a day of national festival in Sri Lanka. The king with a large party of followers went to Mihintale hills (see map at bottom of notes) on a hunting expedition. After testing King Devanampiya intelligence, Mahinda preached the Culahatthipadopama Sutta. At the end of the discourse, the king and his 40,000 entourage embraced the new faith.
The next day the king led the sangha into the palace where after a royal meal Mahinda preached the Petavatthu, the Vimanavatthu and the Sacca-samyutta to the royal household. The royal family was converted to Buddhism after listening to these teachings.
The king offered the Sangha the royal park Mahamegha for their residence and marked the boundaries himself. Thus was established the Mahavihara which became the earliest celebrated monastic institution of Buddhism in Sri Lanka.
King Devanampiya sent his nephew Arittha to Asoka to obtain the help of nuns to enable the women of SL to obtain ordination. King Asoka sent his daughter sanghamitta together with a branch of Bodhi tree to Sri Lanka. Sanghamitta helped start the bhikkuni order in sri lanka. The King built 12 buildings at Upasika-vihara to house Sanghamitta and the newly ordained nuns. He later built the Hatthalhaka nunnery for the nuns. The king took charge of the sacred Bodhi Tree himself and planted it in the Mahamegha garden with great festivities. The Thuparama (stupa) enshrining the right collar bone and other bodily relics of the Buddha was built by the king.
Kings look after the monks’ welfare and monks used their influence over masses to support the kings, there was a mutual understanding that was never explicitly stated. He also set up monasteries and nunneries during his time.