Olympia is located in the flat valley where the Alphios and Kladios rivers meet. All of Hellas used to gather here every four years for the Olympiad games. The Temple of Hera was built in 650 BC and the Temple of Zeus in 470-460 BC. The current remains of the stadium date from 330-320 BC. Other noteworthy structures are the palaistra, philippeion, gymnasium, leonidaion and baths. An Early Christian basilica (400-410 AD) was also found here.The archaeological site of Olympia was declared a World Heritage site by UNESCO in 1989.