Lat. Antium, town (1991 pop. 33,497),  town, Roma province, Lazio (Latium) region, Italy, on a peninsula jutting into the Tyrrhenian Sea. Of uncertain origin, it was founded, according to legend, by Anteias, son of the Greek chieftain Odysseus, and the enchantress Circe. It was a stronghold of the Volsci, an ancient people prominent in the 5th century BC, and was older than Rome, which conquered it in 338 BC. Antium became an all-season resort where many wealthy Romans owned villas. Augustus, the first Roman emperor, was proclaimed “father of the Roman nation” there, and the emperors Caligula and Nero were born there. A key commercial centre under the Volsci, its importance increased after AD 59, when Nero built a port there. The town was destroyed by the Saracens in the early European Middle Ages and was virtually deserted until a new port to the east of the old one was built by Pope Innocent XII in 1698.

Anzio was the scene of heavy fighting late in World War II. On Jan. 22, 1944, the Allies achieved what probably was the most complete tactical surprise of the war by landing in excess of 36,000 troops and 3,000 vehicles before midnight, securing a beachhead only 37 miles (60 km) from Rome. However, the Allied force took so long—most of a week—to consolidate its position that German Field Marshal Kesselring was able to surround the beachhead, keeping its eventual force of six Allied divisions penned there while he mounted a succession of massive attacks on them during February. Only in late May, when Kesselring withdrew most of his troops, were the Allies able to break out of the beachhead (May 25); then the Allied force greatly facilitated the advance on Rome and its capture. Casualties during the four-month operation approximated 25,000 for the Allies and 30,000 for the Axis forces.

Anzio's extensive Roman remains include the ruins of the port, a theatre, and Nero's villa, where valuable works of art, including the famous Greek statue of Apollo Belvedere, were found.

Anzio is now a seaside resort with long sandy beaches and a small port for yachts and fishing boats. It is connected with the main Rome-Naples railway by a branch line from Campoleone.