This mirror was used to produce the sacred flame created by sunlight. The immaculate and immortal flame maintained always lit on altars of the Hestia goddess temples (goddess it was related to) or other cities’ prytaneums.
It was used in each city-state for every blessing, from campaigns’ sacrifices to new altars-homes of colonists. The mirror consisted of four isosceles right triangles of copper or brass bended and soldered in the center, so they would form a concave mirror able to concentrate sunlight to its focus and ignite hollow and dry wood. Described in detail by Plutarch who also mentions four instances (Athens-Aristion, Delphi – Persian Wars – Mithridates – Roman civil war) where it was used when the eternal flame was lost.
