The ancient traveller Pausanias mentions the sanctuary of the Egyptian gods, Isis and Serapis, next to Messene’s theatre. The large complex revealed south of the theatre has been associated with this sanctuary.

It comprised a crypt, an underground cistern, hypocausts (system of under-the-floor heating), as well as rooms decorated with polychrome mosaic floors. After the late 4th cent. AD the cistern was used as a dump for all kinds of disused artefacts; the most prominent among those is the statue of Isis breastfeeding the young Horus.