ALSIUM (mod. Palo), an ancient town of Etruria, 29 m. W. by N. of Rome by rail, on the Via Aurelia, by which it is about 22 m. from Rome. It was one of the oldest cities of Etruria, but does not appear in history till the Roman colonization of 247 B.C., and was never of great importance, except as a resort of wealthy Romans, many of whom (Pompey, the Antonine emperors) had villas there. About 1 m. N.E. of Palo is a row of large mounds called I Monteroni, which belong to tombs of the Etruscan cemetery. Considerable remains of ancient villas still exist along the low sandy coast, one of which, about 112 m. E. of Palo, occupies an area of some 400 by 250 yds. The medieval castle belongs to the Odescalchi family. Near Palo is the modern sea-bathing resort Ladispoli, founded by Prince Odescalchi.
See G. Dennis, Cities and Cemeteries of Etruria, i. 219.