If you have ever read any ancient history, you may have encountered the statement that Ostia, at the mouth of the Tiber, was the port of Rome. Not entirely true. Ostia was a terrible port, and the Tiber is really bad for shipping, so before the end of the Republican period it had become very difficult to bring in enough grain through Ostia to feed the city's immense population. This was the sort of problem the Romans were good at solving, so they went to work providing their city with an alternative port. The hexagonal pond near Rome's airport, above, more than 1600 feet (500 meters) across, is the most dramatic surviving remnant of the alternative port built by the emperors to feed their city. This was called simply Portus.
The work was begun under emperor Claudius and the port was opened by Nero, along with a new road connecting the port to Rome. Then Emperor Trajan improved and expanded the harbor by having the huge hexagonal basin excavated, and a canal built connecting it to the Tiber. From that time until the fall of the western Empire, most of Rome's shipping went by this route. The complex included immense granaries and other warehouses, administrative buildings, a large garrison, and a huge palace.
Archaeologists are investigating Portus in a long-term, multinational project headed by Simon Keays of the University of Southampton. The remains are so immense that uncovering more than a tiny fraction of them using traditional archaeological methods would be impossible. So the project emphasizes remote sensing, especially ground-penetrating radar, some digging with machines, and had digging in a few selected spots.
One of the recent discoveries was an immense building along the north side of the Trajanic harbor, 475 feet (145 meters) long, that the investigators think was a drydock for building or repairing ships.
The outer harbor sported a lighthouse built as a smaller copy of the famous one at Alexandria. The Portus project has many cgi renderings of the port and its buildings on their web site.
When you wonder why medieval and early modern Europeans were so entranced by the ancients and had such respect for even stupid ideas that they found in ancient books, you have to remember that they lived, literally, amidst the ruins of Rome. After Rome fell, no European government could have undertaken a project this big until the late 1700s -- and this was just one of hundreds of such works built by the Romans, from Hadrian's Wall to the Egyptian desert. Many people who lived side by side with the relics of Roman might felt keenly the inferiority of their own power to shape the world, and that bred reverence for classical civilization.