At any rate, all scholars accept that during the 11th century, Pagan consolidated its hold of Upper Burma, and established its authority over Lower Burma. The emergence of Pagan Empire would have a lasting impact on Burmese history as well as the history of mainland Southeast Asia. The conquest of Lower Burma checked the Khmer Empire's encroachment into the Tenasserim coast, secured control of the peninsular ports, which were transit points between the Indian Ocean and China, and facilitated growing cultural exchange with the external world: Mons of Lower Burma, India and Ceylon. Equally important was Anawrahta's conversion to Theravada Buddhism from his native Ari Buddhism. The Burmese king provided the Buddhist school, which had been in retreat elsewhere in South Asia and Southeast Asia, a much needed reprieve and a safe shelter. By the 1070s, Pagan had emerged as the main Theravada stronghold. In 1071, it helped to restart the Theravada Buddhism in Ceylon whose Buddhist clergy had been wiped out by the Cholas. Another key development according to traditional scholarship was the emergence of the Burmese script, believed to have been derived from the Mon script in 1058, one year after the conquest of Thaton. However recent research, though not yet settled, suggests that the Burmese script may have been derived in the 10th century from the Pyu script instead.