After Buddhism was brought to Sri Lanka in the 3rd Century B.C.E, it was chiefly embraced by the Sinhalese, and shortly was established in the heart of the Island. The doctrine gained popularity, and soon after the educating of dhamma and vinaya in major monasteries was widely conducted by monks and laymen. In the latter half of that century Mahinda Thera [Indian monk from Pātalīputra who introduced the doctrine to the Island] addressed King Devānampiyatissa to be the royal sponsor for a council conducted, the first time, in Sri Lanka. The council was conducted in Thūpārama in the city of Anurādapura. ‘Mahāvansa’ scripture states there were 68,000 arahats [the worthy one, or the enlightened one] participated the council. The process, which took 10 months to complete, entailed positive outcome for the doctrine in Sri Lanka; firstly, Theravāda Buddhism is believed to be established the first time outside Jambūdīpa [India]; secondly, soon after Theravada school was also sent across the great ocean from Sri Lanka to establish in Suwannaphūmī, well recognised later as Myanmar, Mon, Siam [Thailand] and Laos.
It is noteworthy to observe that the mission carried out by Mahinda Thera and Sangghamittā Therī is worth to be called the first group of Buddhist missionary who conducted their religious duty outside of India, though it is believed that after the third council [tatiya-sanggīti], Emperor Asoka, the Great, has sent 9 groups of Buddhist missionaries to propagate the doctrine throughout Asia. The two prominent Buddhist figures not only introduced Buddhist teachings and principles to the Sinhalese, but also brought various Indian cultural aspects for instance arts, architecture, and fine-arts into Sri Lanka. It is believed that plentiful Buddhist literatures and commentaries were composed here in this period. As we may have realised that the ‘tipit᷂aka’ [presumably at this stage, while the dispute over the dialect the Buddha preached has still been carried on by scholars nowadays, I believe the ‘tipit᷂aka’ should have been one of local ‘Magadī’ or Kosāla dialects] also was translated into Sinhalese and later was translated back to ‘pālī’- the one we have now, by one of the most famous Buddhist figure named ‘Buddhaghosacariya’ in the 10th B.C.E.
However, Theravāda Buddhism flourished for centuries in Sri Lanka until the 23rd century B.C.E, the doctrine was chiefly affected by disastrously political and social circumstances in Sri Lanka. Consequently, it faded popularity and almost vanished for the second time in history. King Kittirājasingha [2209-2323] observed this negative phenomenon and expressed his great concern. Eventually, it is described by Buddhist chronology in South East Asian tradition that the concern was discussed and suggested by Sarangkara Sāman᷂ero [literally translated ‘novice monk- ascetic who is under 20’, however It seems, perhaps, normal in many traditions to possess such marvellous mythology to revere their belief]. He addressed the issue to the King, and suggested that he should send missionary to Suvannabhūmī [South East Asia] to return Theravāda Buddhist doctrine to Sri Lanka once again.
According several collated chronology of South East Asia, the time mentioned was identical with the flourishing era of, at least, three major Kingdoms in Suvannabhūmi, for instance; Hangsavatī [the city of swan] of Mon which is Pego nowadays; Amarapura [city of eternity] of Myanmar; and Sri Ayodayā [the undefeated city] of Siam. Nonetheless, King Kittirājasingha decided to send his missionary to Ayodayā to bring Saman᷂avansa [Theravāda school of Siam] preceptor to Sri Lanka. We are not curtain the reason of such critical decision. However, King Paramakot᷂ha of Ayodayā agreed with the mission. He then granted the preceptor of Saman᷂avansa School; Upālīthera of Dhammarama monastery and his followers to travel to Sri Lanka. According the Siamese chronicle, Upālīthera arrived at the Island and conducted the baddhasīmā rites [presumably, the ritual process of Buddhism created to legitimate and authorise the authenticity of ordination, literally means ‘set up a boundary’] in pubbārāma [monastery of flower] and dhammikārāma monastery. It is described that plentiful of Sinhalese were ordained in a new Theravāda school introduced by Upālītthera from Siam. The school then established in Sri Lanka and was named after its origin ‘Siamvangsa’.
Nonetheless, Buddhism in Sri Lanka seemed to be affected by some uncertain modern progress and movement which sporadically occurred within that century. By the time ‘Siamvangsa’ successfully established and well embraced, it is believed that several of Theravāda schools were also introduced to the Island, for instance; Amarapuravangsa school from Myanmar; Rāmanvangsa school from Mon. Presumably in the case of teachings and principles of these schools, they seem not different as they emerged and directly influenced from the original Theravāda School in Sri Lanka in the 3rd century B.C.E. However, it is believed that merely ritual practice, and conducts, perhaps, differ from one another. These three Theravādin Schools still are extant and strictly followed in Sri Lanka at the present.