The Porta Capena, the southern gateway in Rome's old Servian Wall (see a stretch of the wall on the Aventine), was the starting point for those journeying to the south.
The Aqua Marcia, a leaky old aqueduct which was in constant need of repairs, crossed above the Porta Capena and was responsible for making it "soaked," madidam.
Nothing remains of the Porta Capena (an arch of the wall gives some idea of what it must have looked like) which was at the head of the Via Appia. This oldest and most important of the Roman roads originally went south as far as Capua, a city north of Naples, and eventually was extended to Brundisium. It was built in 312 BCE by Appius Claudius Caecus, then Censor, and soon after began to be paved with polygonal tufa blocks.