The Metro?n, dedicated to the mother of the gods, Rhea, later re-named Cybele, stood east of the Heraion, below the terrace of the treasuries. This site was used for the worship of Mother Earth, to whom the sanctuary of Gaia was dedicated, and of Eileithyia, a similar deity connected to maternity, as early as the Prehistoric period.

Built in the early fourth century BC, the Metro?n was a small peripteral hexastyle Doric temple with eleven columns at the sides. The columns, 4.63 metres high and 0.85 metres in diameter at the bottom, were made of shell-limestone and covered in white plaster. The temple was divided into three chambers: pronaos, cella and opisthodomos. Both the pronaos and opisthodomos were distyle in antis. The existence of a colonnade inside the cella is uncertain. The architrave and frieze, with its triglyphs and metopes, were of stone, while the timber roof was covered with terracotta tiles. The temple's altar, dedicated to Rhea, was probably situated to its west or on the upper terrace among the treasuries. In the early Imperial period the cult of Rhea/Cybele gave way to that of Augustus and, subsequently, of Roman emperors in general. During the same period a monumental possible cult statue of an emperor represented as Zeus holding a thunderbolt and sceptre was placed inside the sekos; the statue is now displayed in the Olympia Archaeological Museum. Six more imperial statues, three male and three female, discovered in excavation, probably represent Claudius, Titus, Vespasian, Agrippina and Domitia.

Only the temple's stylobate and parts of the entablature have survived and are currently being studied.