The Pagan Empire also changed the history of mainland Southeast Asia. Geopolitically, Pagan checked the Khmer Empire's encroachment into the Tenasserim coast and upper Menam valley. Culturally, the emergence of Pagan as a Theravada stronghold in the face of an expanding Hindu Khmer Empire from the 11th to 13th centuries provided the Buddhist school, which had been in retreat elsewhere in South Asia and Southeast Asia, a much needed reprieve and a safe shelter. Not only did Pagan help restart Theravada Buddhism in Ceylon but the over two centuries of patronage by a powerful empire made Theravada Buddhism's later growth in Lan Na (northern Thailand), Siam (central Thailand), Lan Xang (Laos), and Khmer Empire (Cambodia) in the 13th and 14th centuries possible.