Sri Lanka's Theravada Buddhist tradition played a crucial role in the estavlishment and development of Buddhism in Southeast Asia, particularly as monastic Buddhism had been on the decline in India, before the centres of Buddhist scholarship in the Ganges region finally fell victim to destruction during the Muslim invasions of the late 12th century. It was during this period that the empire of Bagan (Pagan) in Myanmar (Birma) reached is climax under King Chansu II (Sithu II, also known as Narapatisithu). Under his reign the young Buddhist monk Sapada (Chapata)travelled to Sri Lanka in order to study there and to receive a renewed higher ordination to introduce the Sinhalese line of succession in Myanmar. He was from the Mon ethnicitiy, which played a crucial role in transferring the Theravada tradition to the Bagan kingdom. His reform resulted in the establishment of a second order of Theravada Buddhism in Bagan, which became dominant in later centuries. During the 13th century, Sapada's followers, who initially caused only a kind of shism in the Theavada Buddhist culture of Bagan, were even more successfull in missionaries in the Menam region, where the newly established Thai (Siamese) kingdoms were gaining independence from Khmer hegemony. Hence, the Thai adapted the Sinhalese Mahavihara pattern of Theravada Buddhism and made it the official state religion, thereby intentionally turning away from the Hindu religion of the Khmer empire.

However, the Sapada mission and the Thai tradition of Theravada finally succeeded in the Khmer empire, too. According to some reports, one of the companions travelling with Sampada was a son of King Jayavarman VII, who was the first Buddhist king in Cambodia, but an adherent of Mahayanism. After Jayavarman VII's reign during the same period mentioned above, Hinduism had a royal revival in Cambodia inthe second half of the 13th century. But finally Theravada was successfull in Cambodia due to its appeal in rural villages. The Theravada teachings and monsatic line of the Sinhalese sect had been introduced in Cambodia in the course of the 13th century. Unlike Shivaism, Vishnuism, and Mahayana Buddhism, which were imposed from the empire’s elites, the new doctrine was mainly preached to common people. Khmer farmers during the centuries of Hindu and Buddhist state cults had remained to be animistic, sparcely touched by those foreign Indian religions of the Khmer elites. Instead of elaborate court ceremonias, the monks of the Sinhalese tradition prescribed meditation and were devoted to a life of modesty and austerity. Unlike the priestly hierarchy close to the royal family whose political power was in decline, the Theravada monks were in direct contact with ordinary people and managed to stimulate a popular movement. This carried the Khmers, too, into the Theravada fold, until the present day.

Sri Lanka played a crucial role in the development of the Theravada version of Buddhism in Southeast Asia. It has become the predominant religion in Myanmar since the 11th century, where it was reformed in the Sinhalese tradition in the 14th century. In Thailand, conversion to Theravada Buddhism was a means to demonstrate independence from Khmer rule in the 13th century, when the first Thai kingdoms were established. Sri Lankan monks were invited to the then Thai capital, Sukothai. However, the Sri Lankan version of Buddhism, imparted by Thai monks, became prevalent in the Khmer kingdom, too, though slightly later on. Since the 14th century, Theravada has been the national religion of Cambodia. That's the period after the demise of Angkor. During the Angkor period, there had already been some contacts between monks from Sri Lanka and Cambodia. Furthermore, the island of Lanka, as the location of the decisive battle in the sacred Ramayana epic, has become the setting of the most important national Khmer epic, which like in many other literatures of Aoutheast Asia, a version of the said Indian epic. Lanka as a mythical place had already been represented in Khmer art from the Angkor period, most famously at the immensely large carving in the western gallery of Angkor Wat from the mid 12th century. Rama's fight against Ravana, the demon king of Lanka, can also be seen in several lintel carvings from the late 12th cebtury Bayon period, which was mainly Buddhist (Mahayanist, not Theravadic). The photo of such a relief depicting the battle of Lanka is taken from the newly published Preah Khan page, by courtesy of Mr. Sopheak.

Due to the shared Theravada Buddhist tradition, Sri Lanka has mch in common with Myanmar, Thailand, Laos, and Cambodia. Particularly the monastic traditions are intertwined. Strong ties started to develop during the Polonnaruwa period and the 13th century. Although by and large Sri Lanka played a more significant role in the cultural history of the other Theravada countries, traces of influences from Southeast Asia can be seen even in Sri Lanka's heritage sites such as Polonnaruwa. The layout of the Potgul Vihara in the south of Polonnaruwa, with three upper levels of temple terraces, may have been inspired by Khmer architecture. The Satmahal Pasada on the Quadrangle temple platform is a steep step pyramid with niches for Buddha statues, a quite unique structure in ancient Sri Lanka. But it very much resembles Mon architecture of northern Thailand.

The Jetavananarama was a Buddhist monastery during the mid and late Anuradhapura period. Actually, it was the latest of the three giant temples of Anuradhapura, which were also the three largest religious institutions and, apart from the king, the most important land holders with areas of agriculture distributed all over the ancient Sinhalese kingdom. In contrast to the other two pivotal monasteries of Anuradhapura, viz. Mahavihara and Abhayagiri, the youngest one, Jetavanarama, was built in a systematical and symmmetrical ground plan, with the stupa on a wide courtyard in the very centre of  a rectangle of other ceremonial buildings and monks‘ resdidential quarters

With a total height of    122 m and covering 23,3 hectare, the Jetavanarama Dagoba from the 4th century AD is the largest ancient stupa, and with almost 100 million bricks, it’s also the world’s largest construction built of baked stone.

The Jetavanarama of Anuradhapura is not to be confused with the Jetavana monastery in India, which is situated just outside the ancient city of Savatthi (Srvasthi). The Jetavana in northern India was the place where the Buddha gave the majority of his teachings and discourses.   

The foundation of the Jetavanarama in Aniradhapura was the result of sectarian differences between Buddhist monks and even of a sacrilige. According to Buddhist monastic rules incorporated in the Vinaya part of the Holy Scriptures, a consecretad territory of a Buddhist monastery can not be rededicated without the consent of the monks inhabiting it. The Jetavanarama was founded on parts of the temple land of the older Mahavihara, which was expropriated against the resistence of the Mahavihara monks and without proper ceremonies as a result of a conflict between King Mahasena and the clergy of the Mahavihara.

The Aluvihare Temple near Matale is said to have been the location of the 4th Theravada Buddhist Council, which for the first time layed down the Pali Canon of the Holy Scriptures in written form to preserve it for future generations. A museum for palm leaf writings is attached to the ancient temple. The caves have typical Kandyan paintings. A newly decorated cave has gaudy illustrations of hell punishments like a chamber of horrors. Another cave is believed to have been the abode of Buddhaghosa, Church Father of Theravada Buddhism, who lived in the 5th century AD. He is the most famous commentator of the Tipitaka, the Buddhist Holy Scriptures. A stairway along his cave lead to the top of a rock, which is crowned by a small stupa. This is an excellent vantage point overlooking the rocks of the Aluvihare Temple and the surroundings of Matale. The name of the temple, which is situated close to the Kandy-Dambulla-Jaffna road A9, is also spelt Aluviharaya or Aluvihara.