The ancient theater of Ilida (Ilia, Peloponnese) is built in the north of the agora area of the ancient city, on an old upgrade of the river Pinios, which was designed for this purpose. The theater was built in the 4th c. BC. Serious damage, probably by an earthquake during the late Hellenistic period, led to the replacement of the western retaining wall by a newer one. It underwent alterations in Roman times as well.
It has the rather rare peculiarity that its concave (koilon) was made by soil. Stone cladding existed only on the risers that allowed access to its various points, along the lanes, and at a series of stone bearings in its lower part. Six ascending corridors, about one meter wide, paved with river stones (cobbles), divided the concave into seven stands. Strong retaining walls held the embankment of the “koilon” and formed with the side compartments of the stage the two lanes of the theater.