Wat Ong Tu (full name Wat Ong Tu Mahawihan) was built in 1566 by King Sai Setthathirat I (1550-1571) following the relocation of the capital to Vientiane. Located on an ancient religious site reputed to date back to the 3rd century, the original Wat Ong Tu functioned as the king's temple and ceremonies of allegiance to the monarch were held here prior to 1975. The temple is named for the large ‘heavy Buddha’ (Phra Ong Tu) found at the rear of the sim, one of seven Ong Tu Buddha images established by King Sai Setthathirat I during a period of Buddhist renewal throughout the country. The original Wat Ong Tu was destroyed in the 1827-8 war with Siam and has been reconstructed several times since, latterly in 1911. Prince Phetsarath established a Pali School here in 1929 and this still functions today as the Lao Buddhist Institute (see below), a school for monks who come from around the country to study the dhamma. Wat Ong Tu is also the official residence of the Phra Hong Sangkhalat (Deputy Patriarch) of the Lao Buddhist Federation, who presides over the Institute.