Wat Phra Si Sanphet was built in 1448 A.D. on the site which had served for the royal palace from 1350 to 1448 spanning the reigns of King Ramathibodi I to King Sam Phraya. King Borommatrailokanat ordered the wat built to be utilized as a monastic area. His son, King Ramathibodi II constructed two chedi, one to house the remains of his father and the other for his brother, King Borommarachathirat III. A third chedi was built by King Borommrachnophtthangkun for the remains of King Ramathibodi II. A principal viharn (worship hall) was built in 1499 and, in 1500, King Ramathibodi II ordered the casting of a standing Buddha image 16 meters high and covered with gold. This image was called Phra Buddha Si Sanphet