The Altar of Zeus Agoraios (meaning Zeus of the Agora) is a 4th-century BC altar located north-west of the Ancient Agora of Athens, constructed from white marble, 9 m deep and 5.5 m wide. It was one of the first objects to be discovered inside the Agora during the excavations of 1931. Evidence of marks done by masons from the Augustan period show that it was moved from an initial source later identified as the Pnyx located outside the ancient Agora.