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A modern map of the Portus area with the outline of the ancient ports superimposed.
On the right of the map is the modern Tiber River (Tevere) flowing toward the bottom right of the picture. In the upper left is the Leonardo da Vinci airport of Rome.
Note the canal, the Fossa Triana, which flows west from the Tiber into the sea. Above the canal is the hexagonal basin/harbor constructed during the days of Trajan (Bacino di Traiano). To the left of that, outlined by the faint red hash marks is the much larger, and much earlier, basin that was begun by Claudius (Bacino di Claudio). To the left of that basin is a red vertical pointed ellipse where an ancient lighthouse stood on an island—now covered with silt and construction. The ancient coastline was approximately where the yellow star ("you are here") is located—about three miles inland from the present coast.
The map is from a sign at the Portus.