Wat Yai Chai Mongkol was built in the year 1357, by the first ruler of the Kingdom of Ayutthaya – King Uthong. The site was dedicated to the monks of the Pa Kaeo Sect, recently returned from Ceylon where they had been studying under the influential Buhddist teacher Phra Vanarat Maha Thera. The monastery which was born here took its name from them: ‘Wat Pa Kaeo’.