The Polygonal Wall built with asymmetrical interlocking masonry blocks, supports the terrace on which the Temple of Apollo stands. It was built in the second half of the 6^th century B.C (possibly after the destruction of the 1^st temple in 548 B.C but before the building of the Alkmaeonidae Temple), and has a length of 90 metres and is approximately 2 metres shorter today.

The wall was covered with more than eight hundred inscriptions relating to the liberation of slaves, made in the 2^nd and 3^rd century B.C.