But to pass by these matters, which are full of uncertainty, and not so important as to be worth our time to insist on them, the original constitution of the priests, called Pontifices, is ascribed unto Numa, and he himself was, it is said, the first of them; and that they have the name of Pontifices from potens, powerful, because they attend the service of the gods, who have power and command over all. Others make the word refer to exceptions of impossible cases; the priests were to perform all the duties possible to them; if any thing lay beyond their power, the exception was not to be cavilled at. The most common opinion is the most absurd, which derives this word from pons, and assigns the priests the title of bridge-makers. The sacrifices performed on the bridge were amongst the most sacred and ancient, and the keeping and repairing of the bridge attached, like any other public sacred office, to the priesthood. It was accounted not simply unlawful, but a positive sacrilege, to pull down the wooden bridge; which moreover is said, in obedience to an oracle, to have been built entirely of timber and fastened with wooden pins, without nails or cramps of iron. The stone bridge was built a very long time after, when Aemilius was quaestor, and they do, indeed, say also that the wooden bridge was not so old as Numa's time, but was finished by Ancus Marcius, when he was king, who was the grandson of Numa by his daughter. The office of Pontifex Maximus, or chief priest, was to declare and interpret the divine law, or, rather, to preside over sacred rites; he not only prescribed rules for public ceremony, but regulated the sacrifices of private persons, not suffering them to vary from established custom, and giving information to every one of what was requisite for purposes of worship or supplication. He was also guardian of the vestal virgins, the institution of whom, and of their perpetual fire, was attributed to Numa, who, perhaps fancied the charge of pure and uncorrupted flames would be fitly entrusted to chaste and unpolluted persons, or that fire, which consumes, but produces nothing, bears all analogy to the virgin estate. In Greece, wherever a perpetual holy fire is kept, as at Delphi and Athens, the charge of it is committed, not to virgins, but widows past the time of marriage. And in case by any accident it should happen that this fire became extinct, as the holy lamp was at Athens under the tyranny of Aristion, and at Delphi, when that temple was burnt by the Medes, as also in the time of the Mithridatic and Roman civil war, when not only the fire was extinguished, but the altar demolished, then, afterwards, in kindling this fire again, it was esteemed an impiety to light it from common sparks or flame, or from any thing but the pure and unpolluted rays of the sun, which they usually effect by concave mirrors, of a figure formed by the revolution of an isoceles rectangular triangle, all the