The Siyam Nikaya is the oldest of the Sri Lankan monastic fraternities, and its founding illustrates how fragile the ordination lineage of Theravada Buddhism can be.
Re-importing valid ordination
Higher ordination in Theravada requires a quorum of validly ordained monks, and if the lineage lapses it cannot simply be restarted from books. By the eighteenth century the valid higher ordination had died out on the island. In 1753 King Kirti Sri Rajasinha and the reforming monk Welivita Sri Saranankara brought senior monks from Ayutthaya in Siam to Kandy to restore it, and the fraternity founded on that imported lineage took its name from Siam. It centres on the Temple of the Tooth at Kandy and its chapters at Malwatta and Asgiriya.
Caste, and what it produced
Historically the ordination of the Siyam Nikaya was restricted to the highest, govigama, caste. That restriction is not incidental: it is the direct cause of the founding of the later fraternities, the Amarapura and the Ramanna, by and for those excluded from it. The Sri Lankan monastic map, three fraternities rather than one, is therefore in large part a record of a caste dispute worked out through competing ordination lineages.