ALGIDUS, a mountain range of Latium in Italy, between Præneste and the Mons Albanus. On the top of one of these mountains was erected a temple of Diana, to which Horace refers, lib. i. ode 21, "Quæcumque aut gelido prominet Algido;" and lib. iii. ode 23, "Quæ nivali pascitur Algido," &c.