Numa

And if by any chance it goes out, as at Athens during the tyranny of Aristion[*](88-86 B.C. Cf. Lucullus, xix. 6; Sulla, xiii, 3. ) the sacred lamp is said to have been extinguished, and at Delphi when the temple was burned by the Medes, and as during the Mithridatic and the Roman civil wars the altar was demolished and the fire extinguished, then they say it must nor be kindled again from other fire, but made fresh and new, by lighting a pure and unpolluted flame from the rays of the sun.

And this they usually effect by means of metallic mirrors, the concavity of which is made to follow the sides of an isosceles rectangular triangle, and which converge from their circumference to a single point in the centre. When, therefore, these are placed opposite the sun, so that its rays, as they fall upon them from all sides, are collected and concentrated at the centre, the air itself is rarefied there, and very light and dry substances placed there quickly blaze up from its resistance, the sun’s rays now acquiring the substance and force of fire.