portus

The word portus, meaning "harbor, port," was used for the quays that began to be constructed in the 2nd century BCE along the banks of the Tiber River in Rome, to accommodate merchant and military ships (see Museum of Roman Ships) and warehouses and granaries. It also signified Rome's harbor at the mouth of the Tiber, which was almost silted over by the mid-1st century BCE (see Ostia: Harbour City), as well as the harbor town, itself called Portus, both of which were connected to Rome by the via ostiensis. Portus was originally conceived by Julius Caesar and built 2 miles north of Ostia (see map) at the branch of the Tiber called the Fiumicino by Claudius (see harbor plan and the coin of Nero, struck to mark the opening of the new harbor at Ostia, 58-64 CE). In response to the dangers of the exposed moles of Claudius' harbor and increased shipping, in the early 2nd century CE the harbor at Portus was enlarged and given a protected hexagonal inner basin by Trajan (see a reference to this harbor in Juvenal, Satura 12.75-82). A reconstruction of Portus (see plan of the double harbor) was painted in 1970, based on a late 16th century fresco landscape showing the ruined monuments of the town.
In using the plural form, Umbricius' statement embraces all of the above, as no doubt harbor and riverside construction and repair were a constant feature of Roman public works.