ALGIDUM, a town of Latium, in Italy, between Preneste and Alba, near the mountains. On the top of one of these mountains was erected a temple of Diana, to which Horace refers, lib. i. ode 21, "Quacunque aut gelido prominet Algidum;" and lib. iii. ode 23, "Quae nivali pascitur Algidum," &c.