Sirmium

Listen for a moment. Under the hum of traffic and the voices drifting from nearby cafés, there is something quieter here. It is the sound of footsteps on modern paving stones that rest on an ancient Roman city. In Sremska Mitrovica the past does not sit behind a fence on a distant hill. It lies directly under the shops, the courtyards and the gardens. Sometimes it lies only a few spades deep.

This is Sirmium. Today the name means a scatter of excavated sites across a calm Serbian town. For a short and remarkable period, it meant something much larger. At the end of the third century, Sirmium was one of the capitals of the Roman Empire. Emperors lived here. Armies marched out from here. The future of the Mediterranean world was sometimes decided in these streets.

First, consider the setting. The town sits on the Sava River, on the wide flat plain of a region the Romans called Pannonia. That plain matters. Roads ran easily across it, and the river carried boats and supplies. The Danube frontier lay not far to the north and east. Beyond that frontier lived peoples that Rome feared and fought for centuries. A city here was a hinge between the safe interior and the dangerous edge.

The Romans understood this early. A settlement grew here in the first century, and it gained status as Roman rule spread across the region. During the second century the emperor Marcus Aurelius fought long wars against Germanic tribes along the Danube. Ancient writers record that he spent time at Sirmium during those campaigns. It is a striking thought. The philosopher-emperor, famous for his private reflections, may have walked this plain in winter mud.

Now comes the first surprise. Sirmium and the countryside around it produced a remarkable number of Roman emperors. Sources link several of them to this area, including Probus, Constantius the Second and Gratian. Many of these men came from soldier families. They rose through the ranks of the frontier army, not through the old aristocracy of Rome. In the third century, this corner of the Balkans was a breeding ground for the empire's rulers.

That explains what happened next. Around the year 293, the emperor Diocletian divided power among four rulers. Historians call this system the Tetrarchy, meaning rule by four. Each ruler needed a base close to the frontiers he defended. Sirmium became one of those bases, alongside cities such as Nicomedia, Milan and Trier. For a few decades, this provincial town stood among the political centres of the Roman world.

An imperial capital needs imperial buildings. Archaeologists have uncovered the remains of a large palace complex here. Part of it is now protected under a modern roof, so visitors can walk above the excavations. Look down and you will see wall foundations, the outlines of rooms, and fragments of floor mosaics. You may also notice small stacked pillars of brick. These held up floors so that hot air could circulate beneath them — a Roman form of underfloor heating.

Next to the palace, the Romans built a hippodrome, a long track for chariot races. In late Roman capitals, the palace and the racetrack often stood side by side. The emperor appeared before the crowd at the races. The people cheered or jeered, and politics happened in the stands. Much of the track now lies under the modern town. Even so, it helps to picture the scale. Thousands of voices once rose from this ground on race days.

Here is the second surprise. Sirmium mattered to the history of Christianity as much as to the history of empire. In the fourth century, church leaders met here several times. They argued about the nature of Christ, a dispute that divided the empire for generations. Several statements of belief carry the city's name. Earlier, during the persecutions of Diocletian's reign, local Christians died for their faith. Among them was a bishop named Irenaeus, remembered as a martyr of Sirmium.

The city also witnessed moments of crisis. In 379, after a disastrous Roman defeat in the Balkans, Theodosius was proclaimed emperor at Sirmium. He later became the last ruler to govern both halves of the empire. Over the following centuries the Roman hold on the region weakened. Goths, Huns and others crossed the plain. Control of the city passed between Rome, Constantinople and various newcomers.

The final blow came in the late sixth century. The Avars, a powerful steppe people, besieged Sirmium for a long time. Around the year 582, the city surrendered. Accounts suggest that much of the population left, and the great Roman city faded. Over the following centuries a new town grew slowly on the ruins. Medieval and later builders reused Roman stone, so fragments of the ancient city are still hidden in later walls.

That layering is what makes a visit here unusual. You will not find one grand ruin standing alone. Instead, you will find excavations in several places around the centre, along with finds in the local museum. Inscriptions, sculpture, coins and everyday objects help fill in the picture. Walk slowly between the sites. Notice how the modern street pattern sometimes follows older lines. The Roman city is not gone. It has simply been built over again and again.

So pause here for a moment before you move on. Look at the low walls in front of you and the thin red bricks set into them. Ordinary people laid those bricks by hand, under orders from an empire that believed it would last forever. Then listen again. The traffic, the café voices, the river somewhere nearby. As you walk away through Sremska Mitrovica, remember that every street here has two levels — the town you can see, and Sirmium beneath it.