The period of Angkor is the period from approximately the latter half of the 8th century AD to the first half of the 15th century. If precise dates are required, the beginning may be set in 802 AD, when the founder of the Khmer Empire, Jayavarman II pronounced himself universal monarch (chakravartin) and declared independence from Java, and the end may be set in 1431 AD, when Thai invaders from the kingdom of Ayutthaya sacked Angkor and caused the Khmer elite to migrate to Phnom Penh.In any study of Angkorian architecture, the emphasis is necessarily on religious architecture, since all the remaining Angkorian buildings are religious in nature. During the period of Angkor, only temples and other religious buildings were constructed of stone. Non-religious buildings such as dwellings were constructed of perishable materials such as wood, and so have not survived.The religious architecture of Angkor has characteristic structures, elements, and motifs, which are identified in the glossary below. Since a number of different architectural styles succeeded one another during the Angkorean period, not all of these features were equally in evidence throughout the period. Indeed, scholars have referred to the presence or absence of such features as one source of evidence for dating the remains.