Fossa Traiana

About

Artificial canal (c. 90 m wide) linking the Portus basins to the Tiber and the sea, cutting off the wedge of land between it and the river's main channel to create the Isola Sacra. Sources disagree on strict attribution: despite the name 'Fossa Traiana,' the canal's origin is tied to Claudius's flood-relief/harbor-access works of the 40s CE (an inscription of 46 CE mentions it), though tradition and its surviving name credit Trajan, whose hexagonal-basin project of c. 100-112 CE certainly reused, enlarged, and depended on it as the link to the Tiber and sea. Whichever emperor's work is emphasized, the canal was long-since dug and functioning by 117 CE. Medieval Fiumicino ('little river') preserves its name. Coordinates are an approximate midpoint of the canal's course between Portus and the river; low positional precision.

What happened here

Cut to shorten a journey, to bypass a river mouth that silts, or to drain ground that floods. Digging is done by soldiers or by contracted labour in seasons when the water is low, and the spoil is banked along the sides to make a towpath. Barges are hauled by men or oxen, moving grain, stone, timber and wine at a fraction of the cost of the same distance by road. Sluices control the level where the canal meets a tidal river. Maintenance is endless — silt, weed and collapsed banks — and a canal that is not dredged returns to marsh within a generation. Towns along it grow fast, and the tolls charged at each end are worth having.

Sources

• https://en.wikipedia.org/wiki/Fiumicino
• https://www.ostia-antica.org/portus/t001.htm
• Russell Meiggs, Roman Ostia (Oxford, 2nd ed. 1973)