Pali became the "sacred language" of Buddhism in the Theravada countries Sri Lanka, Thailand and Burma. Just as in present-day Sri Lanka the suttas are chanted in Pali followed by a sermon in Sinhala, so also in the past preaching in the vernacular was the norm. It is estimated that the texts themselves were preserved in oral form in northern India well into the fifth century CE, and Chinese monks who travelled to India in search of authentic scriptures often had great trouble finding written texts that they could take home with them. Buddhism may be counted as one of the great scripture-producing religions. In China, each school tended to proclaim its favoured scripture as the final flowering of the dharma for which all the others were mere preparation. The Lotus Sutra regards itself as containing the "One Vehicle" (ekayana) which includes Hinayana, Mahayana and Vajrayana, which Chih-i took to be irrefutable proof of its superiority.