The Pontine Marshes (/ˈpɒntaɪn/ PON-tyne, US also /ˈpɒntiːn/ PON-teen; Italian: Agro Pontino [ˈaːɡro ponˈtiːno], formerly also Paludi Pontine; Latin: Pomptīnus Ager [sg.] by Titus Livius, Pomptīna Palus [sg.] and Pomptīnae Paludes [pl.] by Pliny the Elder) is an approximately quadrangular area of former marshland in the Lazio Region of central Italy, extending along the coast southeast of Rome about 45 km (28 mi) from just east of Anzio to Terracina (ancient Tarracina), varying in distance inland between the Tyrrhenian Sea and the Volscian Mountains (the Monti Lepini in the north, the Monti Ausoni in the center, and the Monti Aurunci in the south) from 15 to 25 km (9+1⁄2 to 15+1⁄2 mi). The northwestern border runs approximately from the mouth of the river Astura along the river and from its upper reaches to Cori in the Monti Lepini.
The former marsh is a low tract of mainly agricultural reclaimed land created by draining and filling, separated from the sea by sand dunes. The area amounts to about 80,000 hectares (200,000 acres). The Via Appia, a Roman military road constructed in 312 BC, crosses the inland side of the former marsh in a long, straight stretch flanked by trees. Before then, travelers had to use the Via Latina along the flanks of the mountains; Terracina could not be reached across the marsh.
