Some 130 kilometres south of Phetchabun, on Highway 21, is the Si Thep Historical Park. It contains the ruins of ancient Phetchabun, encompassing Si Thep ancient town, originally called Mueang Aphai Sali. It is believed to have been built during the boom years of the ancient Khmer empire, 1,000 years old. The historic town is surrounded by a moat and a mound; inside, ponds and swamps dot the compound.[6]