The coast of Lazio is mainly composed of sandy beaches, punctuated by the headlands of Circeo (541 m) and Gaeta (171 m). The Pontine Islands, which are part of Lazio, are off Lazio's southern coast. Behind the coastal strip, to the north, lies the Maremma Laziale (the continuation of the Tuscan Maremma), a coastal plain interrupted at Civitavecchia by the Tolfa Mountains (616 m). The central section of the region is occupied by the Roman Campagna, a vast alluvial plain surrounding the city of Rome, with an area of approximately . The southern districts are characterized by the flatlands of Agro Pontino, a once swampy and malarial area, that was reclaimed over the centuries.