The Pāli name for Siam. There was very close relationship between Ceylon and Siam from the middle ages. For details see J.R.A.S. (Ceylon) xxxii.190ff.
When Buddhism fell on evil days in Ceylon, the kings of that Island turned to Siam for help in the restoration of the Faith. Kittisirirājāsīha obtained copies of the Mahāvamsa from Siam and completed the chronicle down to his day (Cv.xcix.78f). With the help of the Olandā (Dutch), he sent an embassy to Ayojjhā - capital of Dhammika, king of Siam - asking that a chapter of monks might be sent to Ceylon. Ten monks were sent, with Upāli and Ariyamuni at their head, together with many books and other gifts. The monks took up their residence in the Pupphārāma in Sirivaddhanapura (Kandy), and, under the king's patronage, the ceremony of ordination was held on the 2296th year after the Buddha's death, on the full moon day of Ashālha.
Some time later, Dhammika again sent a chapter led by Visuddhācariya and Varañānamuni. As a token of his gratitude, Kittisirirājasīha sent to Dhammika a model of the Buddha's Tooth Relic in Kandy, together with various other gifts. Dhammika returned his courtesy by sending various books not to be found in Ceylon, a replica of the Buddha's footprint found on the Saccabaddha Mountain, etc. Cv.c.63ff., 136 ff.