Portus

Listen for a moment. Somewhere overhead, a jet climbs out of Fiumicino airport. Below it, the ground is quiet: umbrella pines, tall grass, and long walls of Roman brick, warm orange in the sun. You are standing in what was once the busiest harbour of the ancient Mediterranean. Today it sits several kilometres from the sea, surrounded by fields. That distance is the first surprise of Portus. The coast has moved, and the harbour was left behind.

Why did Rome need a port here at all? The city of Rome sits upriver on the Tiber, and it fed a population of perhaps a million people. Grain, oil, wine and stone arrived by sea from Egypt, North Africa, Spain and Gaul. The old river port at Ostia, a short distance south, could not handle the largest cargo ships. Its river mouth silted up. Big ships often had to anchor offshore and unload into smaller boats. That was slow, costly and dangerous.

The emperor Claudius decided to solve the problem in the middle of the first century. His engineers dug a large artificial harbour into the coastline, north of the Tiber mouth. They protected it with two long curving moles, which are breakwaters built out into the sea. Canals linked the harbour to the river, so goods could travel up the Tiber to Rome on barges. The project was enormous for its time. Work continued for years and was finished under Nero.

Here is a detail that many visitors miss. The ancient writers Suetonius and Pliny the Elder describe how a lighthouse was built at the harbour entrance. Its foundation was a huge ship, deliberately filled and sunk. This was the vessel that had carried an Egyptian obelisk to Rome for the emperor Caligula. That obelisk still stands today in Saint Peter's Square in the Vatican. So a piece of this harbour's story is visible in the heart of the city.

Claudius's harbour had one serious weakness. It was open to the sea and exposed to storms. The historian Tacitus records that a storm wrecked around two hundred ships inside it. The solution came under the emperor Trajan, in the early second century. His engineers dug a second basin further inland, sheltered and calm. They gave it an unusual shape — a perfect hexagon. Each of its six sides runs for several hundred metres.

That hexagon still exists. It is filled with water, and locals call it the Lake of Trajan. Seen from an aircraft coming in to land at Fiumicino, its six straight edges stand out clearly in the landscape. Passengers often notice it without knowing what it is. On the ground, the scale is harder to grasp. The water stretches out flat and still, framed by trees, and it can feel more like a park than a harbour.

Why a hexagon? Scholars still discuss the reasons. One practical answer is that the six sides gave a long quay frontage for ships to moor and unload, while every point stayed reachable. Around the basin stood warehouses, offices, temples and docks. Columns along the quays carried numbers, which may have helped ships find their assigned berths. Imagine the noise: ropes creaking, dockworkers shouting in many languages, and amphorae, the clay jars of the ancient world, knocking together in carts.

As you walk, look closely at the brickwork. Roman builders often used brick facing over a concrete core. Some of the long walls here belong to the great warehouses, built to store grain and other goods before they went up the river. Their size tells you how much food moved through this place. The supply of Rome was a political matter. An emperor who let the city go hungry risked riots, and Portus was part of his insurance.

Archaeologists have worked here intensively in recent decades. A long-running research effort known as the Portus Project, led by the University of Southampton with Italian and British partners, has surveyed and excavated across the site. Their work identified large buildings near the basin, including what appears to be an imperial palace complex, and a vast structure that may have served as shipsheds or warehouses. Much of ancient Portus still lies under the fields. Every season of digging adds new pieces.

Portus did not stay a simple dock. Over time it grew into a town in its own right, with its own people, churches and walls. In the fourth century, under the emperor Constantine, it gained independence from neighbouring Ostia. As the western empire weakened, the harbour became a strategic prize. During the wars of the sixth century, armies fought for control of it, because whoever held Portus could cut off Rome's supplies.

Then came the slow decline. Without constant dredging, the river kept carrying sand and silt to the sea. The shoreline crept outward, year after year, century after century. The harbour basins lost their link with open water. People moved away, and the ruins were gradually buried and farmed over. One canal survived in another form, though. The channel known in antiquity as the Fossa Traiana still runs today as the canal at Fiumicino, used by fishing boats.

Not far from here lies the Isola Sacra necropolis, the cemetery of the ancient harbour town. Its tombs belonged to ordinary working people — merchants, craftsmen and their families. Some carry small reliefs showing their trades. If you have time, it adds a human scale to what you see at Portus. Here you see the engine of the empire. There you meet some of the people who kept it running.

Before you leave, stand still for a minute near the water or beside one of the old walls. Notice how quiet it is, apart from the birds and the planes. It is a strange pairing. Two thousand years ago, ships from across the known world arrived here. Today, aircraft from across the world arrive overhead, just as they always have in this corner of Rome. As you walk back, look at the flat land around you, and remember that much of it was once the sea.