It was founded around 500 BCE to placate Cybele, who had visited a plague on Athens when one of her wandering priests was killed for his attempt to introduce her cult. The account may have been a later invention to explain why a public building was dedicated to an imported deity, as the earliest source is the Hymn To The Mother Of The Gods (362 CE) by the Roman emperorJulian.1
The Metroon in the Ancient Agora of Athens was originally used as the meeting chamber of the boule or city council. At the end of the 5th century BCE, when a new Bouleuterion was built, the building was dedicated to the mother goddess. The Metroon also housed the official archives of the city.2
Part of the complex of Olympia, and sited immediately below the terrace which houses the Treasuries, is the late 4th/early 3rd century Metroon.3
^Roller, 1999. pp. 162 - 167; Roscoe, p. 200; Robertson, in Lane, p. 258.