Ancient town of south-central Thailand founded in the 5th-7th centuries and later incorporated into the Khmer empire of Angkor in the 10th or 11th century. It became an important provincial capital. One of Thailand's major historical sites, the city retains numerous buildings from the early periods. The Prang Sam Yod (Three-Spired Sanctuary), the symbol of the Lop Buri region, was built by the Khmers. Other places of interest include the temple complex of Wat Phra Si Ratana Maha That (1157) and the remains of the Nakhon Kosa temple. It later became an active center within the kingdom of Ayutthaya (founded 1351) and was the summer capital of the Ayutthaya king Narai (reigned 1657-88). Thereafter the city declined, and many of its buildings decayed.