Shrine of Zeus Hypsistos
From Project Athinai
A shrine dedicated to Zeus Hypsistos existed on the Pnyx during our period of reference. It was located above the assembly place immediately to the southwest of the emplacement of the future bema (platform) built around 330 BC.
The open-air sanctuary was carved into the rock. Several niches carved into the walls contained votive offerings.
A big rectangular niche was added during the Roman period to house the cult statue of Zeus.
Travlos, John, Pictorial dictionary of Ancient Athens, Books that matter, New York, 1971, p. 569