The kingdom of Ayutthaya existed between 1350 and 1767 A.D. and was founded by its first ruler King Ramathibodi I. The prior and short-lasting kingdom of Sukhothai to the North was absorbed into Ayutthaya. Theravada Buddhism became the official religion early on and King Ramathibodi I also compiled a legal code.
The Thai rulers of Ayutthaya were absolute monarchs. They assumed the title of 'devaraja' (god-king) as opposed of the title of 'dhammaraja' during the Sukhothai period. As devaraja the King became an earthly incarnation of the lord Shiva.
To the West, the Kingdom of Ayutthaya faced its most formidable adversary. The Burmese overrun Chiang Mai and Laos in the mid 16th century, and captured the city of Ayutthaya for a first time in 1569. They installed a vassal king at Ayutthaya. However, the control over Ayutthaya by the Burmese was shortlived, and King Naresuan the Great (1590-1605) managed to defeat the Burmese and reinstall authority.
About two centuries later, the Burmese converged again on Ayutthaya. After a lenghty siege, the city of Ayutthaya fell and was utterly destroyed. This destruction of art treasures, buildings, historical records makes it difficult nowadays to truly visualize the splendour of Ayutthaya in its glory days.