Some remains of archaic buildings, discovered under the xystus, were possibly related to a sanctuary dedicated to Demeter and indicate the sanctity of the area from earlier times.
One comprised the xystus and the "paradromis", i.e. an auxiliary corridor used by the runners, and the other the palaestra with all its annexes, such as the changing rooms and the baths.
It was initially formed by a Doric colonnade made of poros stone, dated to the 4th century and consisting of 83 columns.
On the lower terrace was situated the palaestra, comprising a square central court of the "impluvium" type, surrounded by porticoes divided in rooms.
In the Roman period a bath with hot water was built also close to the Gymnasium, thus offering an extra luxury to the athletes.