U Thong is a city located in Thailand. It is historically significant as the seat of King U-thong, also known as King Ramathibodi I, who served as the founder and first monarch of the Ayutthaya Kingdom from 1351 to 1369.
King U-thong is regarded as a pivotal figure in Thai history for unifying the rival power centers of Lopburi (Lavo) and Suphan Buri (Suphannaphum). His reign established a centralized state that dominated mainland Southeast Asia for more than four centuries.