right|250px|thumb|Hunting in the Pontine Marshes, oil on canvas by [[Horace Vernet, 1833]]
thumb|250px|Lake Fogliano, a coastal lagoon in the Pontine Plain
thumb|250px|[[Terracina today, looking northward at the promontory: the former marsh to the right of it stretches over the horizon. In the lower right corner, the Volscian Mountains descend to the edge of the narrow strip on which Terracina is situated.]]
thumb|250px|National Park of Circeo, on the coast of the Pontine Fields: the view is an aerial photograph. Visible in the foreground is Lago di Fogliano, one of the laghi costieri, "coastal lagoons".
The Pontine Marshes ( , ; , formerly also ; [] by Titus Livius, [] and [] 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 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