The friendly ties between Sri Lanka and Cambodia go back many centuries, with the earliest traces of religious relations going back to the beginning of the 6th century. Historians have pointed out that the Chulavamsa records that Cambodia and Sri Lanka had close political and cultural contacts in the 12th century.
Eminent historian Michael Wright, in a recent paper, listed several architectural evidences to show that the Sinhala form of Buddhism, reformed by King Parakramabahu I, and the Lankavamsa ordination may have arrived at Angkor during the reign of Jayavarman VII.
Wright suggests that from Angkor, the Lankavamsa spread north and west into what is now Thailand and Laos, carrying with it the Angkor prestige, sacred script and the cult of divine kingship. As testimony he cites that the Pali language was consistently written in Khmer script in the region for a long period of time. If Buddhism arrived in Thailand first, he argues that Pali would have been written either in Sinhala or Siamese script. He has pointed out that the RatanabimbaVamsa (History of the Emerald Buddha) claims that the Emerald Buddha image, the Thai national palladium came from Lanka, first to Angkor and only later travelled to Thailand and Laos.
In full: http://www.sundayobserver.lk/2019/08/11/opinion/cambodia-sri-lanka-ties-strengthened