Different opinions exist about when, exactly, Buddhism reached that part of the world now officially known as Thailand. Some scholars say that Buddhism was introduced to Thailand during the reign of Asoka, the great Indian emperor who sent Buddhist missionaries to various parts of the then known world. Others are of the view that Thailand received Buddhism much later. Judging from archaeological finds and other historical evidence, however, it is safe to say that Buddhism first reached Thailand when the country was inhabited by a racial stock of people known as the Mon-Khmer who then had their capital, Dvaravati, at a city now known as Nakon Pathom (Sanskrit: Nagara Prathama), about 50 kilometers to the west of Bangkok. The great pagoda at Nakon Pathom, Phra Pathom Chedi (Prathama cetiya), and other historical findings in other parts of the country testify to this fact as well as to the fact that Buddhism, in its varied forms, reached Thailand at four different periods, namely:
Theravada or Southern Buddhism
Mahayana or Northern Buddhism
Burma (Pagan) Buddhism
Ceylon (Lankavamsa) Buddhism
We shall now proceed to study each of these periods in detail.