West of the Altis, between the Theokoleon and the Greek baths, lies the hero?n. Built in the second half of the fifth century BC as the sweat room (ephidroterion) of the baths, it became a hero?n, or monument to a hero, in the Hellenistic and Roman periods.

The hero?n was a small square building consisting of two rooms and an oblong portico, 5.10 metres wide. The north room enclosed a circular structure, c. eight metres in diameter. Both north and south rooms were entered from the west through the portico, which had four columns on its west fa?ade. In the Classical period when the building was a bath, the north room functioned as a sweat room, while the south room probably housed the water heating system. Inside the circular room was a small altar of ash and clay, only 0.38 metres high, 0.54 metres long and 0.37 metres wide. The word 'hero' flanked by olive branches was inscribed on the altar, and because the altar's surface was regularly renewed the inscription was re-painted (often with different spellings). The altar was dedicated to an unknown hero. Pausanias (V, 15, 8) records another altar, dedicated to Pan, in the same space.