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,[1] Pomptīna Palus [sg.] and Pomptīnae Paludes [pl.] by Pliny the Elder[2][3]) 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).[4] 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).[5] 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.
Further southward along the coast as far as Minturno is another stretch of former coastal marsh called the South Pontino, the largest section being between Terracina and Sperlonga, as far inland as Fondi. It was part of ancient Latium adiectum and still belongs to Lazio. Bordered by the Aurunci Mountains, this land is mainly reclaimed, as well, but the more frequent incursion of hills permitted more dense settlements. Leaving Terracina, the Via Appia crosses it, as well.
The marsh was an extensive alluvial plain at about sea level (some above, some below) created by the failure of the streams draining the mountains to find clearly defined outlets to the sea through the barrier dunes.[4] Above sea level, it was a forested swamp; below, it was mud flats and pools. Sparsely inhabited throughout much of their history, the Pontine Marshes were the subject of extensive land reclamation work performed periodically. The tribe of the Volsci began with minor draining projects in the vicinity of Tarracina in connection with their occupation of it in the pre-Roman period.
The road proved difficult to keep above water. Under Augustus, a compromise was reached with the construction of a parallel canal. The part of the marsh above sea level was successfully drained by channels, and new agricultural land of legendary fertility came into being. Whenever the channels were not maintained, the swamp reappeared. Meanwhile, frequent epidemics of malaria at Rome and elsewhere kept the reclamation issue alive. Under Benito Mussolini's regime in the 1930s, the problem was nearly solved by placing dikes and pumping out that portion of the marsh below sea level. It continues to need constant maintenance. Italian confidence in the project was so high, the city placed by Mussolini in 1932 in the center of the marsh, Latina, became the capital of a new province, Latina.