The Sanctuary of Zeus Polieus was a no walled open-air sanctuary dedicated to Zeus Polieus (city protector) around 500 BC on the Acropolis of Athens, sited to the Erechtheion's east. None of its foundations have been discovered and its trapezoid plan and many entrances have been worked out from rock cuttings on the acropolis. The eastern area of the sanctuary is thought to have housed the oxen for the annual Bouphonia or ox-sacrificing.