Lavinium was a port city of Latium, 53 km (33 mi) to the south of Rome, at a median distance between the Tiber river at Ostia and Anzio. The coastline then, as now, was a long strip of beach. Lavinium was on a hill at the southernmost edge of the Silva Laurentina, a dense laurel forest, and the northernmost edge of the Pontine Marshes, a vast malarial tract of wetlands. The basis for the port, the only one between Ostia and Anzio, was evidently the mouth of the Numicus or Numicius river.