The site of Olympia, in a val­ley in the Pelo­pon­nesus, has been inhab­it­ed since pre­his­toric times. In the 10th cen­tu­ry B.C., Olympia became a cen­tre for the wor­ship of Zeus. The Altis &ndash, the sanc­tu­ary to the gods &ndash has one of the high­est con­cen­tra­tions of mas­ter­pieces from the ancient Greek world. In addi­tion to tem­ples, there are the remains of all the sports struc­tures erect­ed for the Olympic Games, which were held in Olympia every four years begin­ning in 776 B.C.