PONZA, the principal island of a small volcanic group, the Pontian, Pontine, or Pontinian Islands (Insulae. Pontiae, Isole Pome), which lie 20 miles off the Circeian promontory (Monte Circello), the northern end of the Gulf of Gaeta, on the west coast of Italy. The two smaller islands are Palmarola (ancient Pαlmαriα) and Zannone (Simonia), neither inhabited. Ponza is 5 miles long and very irregular in outline; its soil is fertile; and in 1881 it had 3828 inhabitants. The old fortress is used as a penal establishment.

A Roman colony with Latin rights was settled on Pontia in 313 b.c. Under the empire the island was a place of banishment for political offenders. Nero, the eldest son of Germanicus, here perished by command of Tiberius; here the sisters of Caligula were confined; and here, or in Palmaria, Pope Sylverius died. A Benedictine monastery was built on Ponza, and in 1572 Cardinal Farnese, as commendatory of the monastery, claimed to exercise lordship over the island. From the duke of Parma, who obtained possession in 1588, the feudal authority passed with Elizabeth to Philip V. of Spain. Ferdinand IV. attracted the inhabitants of Torre del Greco to the island by gifts of land and money. During the first French empire it was occupied and fortified by the English and Sicilian forces.

See TricoH, Monografie, per le isole del gruppo Ponziano, Naples, 1855; Mattei, L'Archipelago Ponziano, Naples, 1857; and Doelter, Vorläufige Mittheilung über den geol. Bau der Pontinischen Inseln, Vienna, 1875.