Before Sukhothai this land was Mahāyāna for centuries — the history school leaves out
Summary
Many of the Saturday Buddhas in Thai temples — the ones cradling a medicine jar — are Bhaiṣajyaguru, the Medicine Buddha of the Mahāyāna, who appears nowhere in the Pali Canon.
Mahāyāna reached Suvarṇabhūmi by two routes. By sea it came with Srivijaya, where the pilgrim Yijing counted monks in the thousands and told Chinese monks to study Sanskrit here before going on to India.
By land it came with the Khmer, who left Phimai — older than Angkor Wat — the three-towered prang at Lopburi, and the 102 royal hospitals of Jayavarman VII.
Then it turned over. Mahāyāna fell with the courts that had paid for it, its source at Nālandā was destroyed, and Lankan Theravāda came in through Nakhon Si Thammarat and up to Sukhothai.
It did not disappear. It survives in the Sanskrit spellings of everyday words, in the amulets people wear, in Jatukham Rammathep, and in Guanyin — the same bodhisattva as the bronze at Chaiya.
Key points
The Saturday Buddha is a Mahāyāna figure
The one holding a medicine jar is Bhaiṣajyaguru, who is not in the Pali Canon at all.
Two routes, not one
By sea with Srivijaya, by land with the Khmer — different paths leaving different traces.
This was once a place others came to study
Yijing told Chinese monks to stop and learn Sanskrit in Suvarṇadvīpa first, and Atiśa studied here twelve years before going north to restore Buddhism in Tibet.
The switch had political causes
Mahāyāna fell with the courts that funded it and with the destruction of Nālandā, not because it lost an argument about doctrine.
The schools all came after the Buddha
He was neither Theravādin nor Mahāyānist, and this teaching has one taste: the taste of release.