Civitas Classis is the name of the military harbour of Ravenna, founded by Augustus (classis is Latin for fleet). Ravenna was surrounded by swamps, just like Ostia (and the workers who, in modern times, drained the marshes of Ravenna later migrated to Ostia, where they did the same). The city is famous for its monuments from late antiquity.
The harbour was connected with Ravenna and the Adriatic Sea by canals. From Ravenna the canal led to Aquileia. Quays with a length of ca. 3 kms were built, lined by store buildings and suited for 250 ships. About 10.000 marines were stationed here. The classis Ravennatis and the classis Misenensis in the Bay of Naples were both under the command of a prefect.