Castra Praetoria

Start with the brick. Put your eye close to the wall and you will see thin, flat bricks laid in long, tight rows, with pale lines of mortar between them. The surface is uneven, patched and darkened by traffic and rain. Cars pass a few metres away. Buses grind their gears. And yet this is Roman work, nearly two thousand years old, still standing at the edge of a modern street.

This is the Castra Praetoria, the camp of the Praetorian Guard. The word castra simply means a military camp, and praetoria comes from the praetor, the old Roman word for a commander. For about three centuries, this enclosure housed the soldiers who protected the emperor. They were also the soldiers who, more than once, decided who the emperor would be.

The camp was built under the emperor Tiberius, in the early first century, around the year 23. The driving force behind it was Sejanus, the commander of the Guard and one of the most ambitious men in Rome. Before this, the guardsmen were spread across lodgings in the city and nearby towns. Sejanus gathered them into a single fortified base. It was a practical decision. It was also a political one, because thousands of trained soldiers in one place, close to the city, made the Guard's commander very powerful indeed.

Sejanus did not enjoy that power for long. Within a few years he fell from favour and was executed. But the camp he created outlived him by centuries. Look at where you are standing. You are on the northeast edge of the ancient city, on high, open ground. In Roman times this area sat just outside the dense centre. It was close enough to march into the Forum quickly, and far enough away to keep the soldiers separate from daily city life.

The plan of the camp followed a familiar Roman pattern. It was a large rectangle with rounded corners, a shape often compared to a playing card. Inside, there were barracks, storerooms, and shrines. Gates opened on each side. Much of the interior is gone now, built over by later structures. What survives most clearly is the outer wall, and that wall is the main thing to see here.

Now for a detail many visitors miss. Look carefully at the upper part of the wall in the better preserved sections. In several places you can make out a line of old battlements, the notched tops of the original wall, now buried inside later brickwork. The first wall was lower. Later builders raised it, and instead of removing the old battlements, they simply filled the gaps and built on top. The old wall sits inside the new one, like a fossil in stone.

Why was the wall raised? In the third century, the emperor Aurelian began a new defensive circuit around the whole city, now called the Aurelian Walls. Rome felt threatened by invasions on the frontiers. Instead of building a new section here, the engineers used the camp itself. Its outer walls became part of the city's defences. That is the main reason so much of it still stands. You may also notice outlines of old gateways that were later bricked up. Those blocked arches mark entrances that were closed when the walls became a city defence.

The soldiers who lived here were an elite force. They earned better pay than ordinary legionaries and served in the capital rather than on distant frontiers. Their loyalty was supposed to belong to the emperor. In practice, it often belonged to whoever paid them best. When the emperor Caligula was murdered in the year 41, guardsmen found his uncle Claudius in the palace and brought him here, to the camp. The Guard declared him emperor, and the Senate had little choice but to accept it.

The most notorious episode came in 193. The Guard murdered the emperor Pertinax after only a few months on the throne. According to the Roman historian Cassius Dio, who lived through these events, the soldiers then offered the empire to the highest bidder. A wealthy senator named Didius Julianus made the best offer and became emperor. His reign lasted only about two months. Shortly afterwards, the new emperor Septimius Severus dismissed the guardsmen and replaced them with soldiers loyal to him.

The end came with Constantine. In 312, he defeated his rival Maxentius at the Battle of the Milvian Bridge, just north of Rome. The Praetorian Guard had fought for Maxentius. Constantine did not reform them this time. He disbanded the Guard completely. The inner wall, the side facing the city, was demolished. The outer walls remained, because by then they were part of the city's defences. So the walls you see survived because the city needed them, not because the Guard did.

It is worth thinking about the contrast here. Many famous Roman sites are temples, theatres, and arenas, places of worship or entertainment. This one was a barracks, built for daily routine and discipline. Soldiers trained, ate, slept, and waited here for orders. The wall has no marble decoration and no carved inscriptions on display for visitors. It is plain military brickwork, designed to be solid and to last.

Today the site still has official and military uses. Part of the old camp area is occupied by Italian military buildings, and the National Central Library of Rome stands nearby, on part of the ancient enclosure. So the space is still used by the state, nearly two thousand years after Sejanus first gathered his soldiers here. Access to the interior is limited, and the best experience is a slow walk along the outside of the walls. The streets around it are named after the camp, so you will see Castro Pretorio on signs and metro maps.

As you walk along the wall, notice how the street follows its line. The modern road bends where the Roman corner turns. Trees grow at the base of the bricks. Pigeons sit in the small holes left by ancient scaffolding. Commuters hurry past without looking up. Termini, the main railway station, is only a short walk away, and its noise reaches you here.

Before you go, step back far enough to see a long stretch of wall at once. Find the line where the old battlements meet the newer brick above them. That line marks the change from a guard camp to a city wall. Then turn and look at the traffic, the apartment blocks, and the people waiting at the bus stop. The wall has stood beside all of it, quietly, through every change Rome has seen.