Aurelian Walls (271): The Fortification of Ancient Rome

The Aurelian Walls are the defensive walls built around Rome from AD 271 under the emperor Aurelian. After centuries in which the capital of the empire had needed no fortifications, raids into Italy during the Crisis of the Third Century persuaded Aurelian to enclose the city with a brick circuit about 19 kilometres long. Strengthened by later rulers, the walls defined the limits of Rome until the 19th century, and around two-thirds of them still stand today.

A city without walls

Rome’s earlier defences, the so-called Servian Wall, dated mainly from the 4th century BC, after the Gallic sack of the city. As Rome’s power grew, the city spread far beyond that circuit, and for most of the imperial age it had no real need of walls. The frontiers were hundreds of kilometres away, guarded by the legions, and the city’s safety was a symbol of the Roman peace.

That confidence was shaken in the mid-3rd century. Germanic raiders crossed the Alps several times, and in 270–271 the Juthungi and Alamanni invaded northern Italy. Aurelian was defeated near Placentia (Piacenza) before winning victories at Fano on the Metaurus river and near Ticinum (Pavia). News of the invasion caused panic and unrest in Rome itself. There was also a serious revolt of the workers of the imperial mint in the city, which Aurelian suppressed with heavy loss of life, according to later sources. The emperor needed both to protect the capital and to show that he was in control.

Construction

Aurelian ordered the walls in 271, before leaving for his campaigns against Palmyra, described in Zenobia and the Palmyrene Empire. The ancient sources say little about the work. It was completed under Probus, probably by about 280, a few years after Aurelian’s death in 275.

The original wall was built of concrete faced with brick, about 3.5 metres thick and around 6 to 8 metres high. Square towers projected from it at intervals of about 100 Roman feet, roughly 30 metres, giving a total of some 380 towers. The main gates, numbering around 18, were placed where the great roads left the city, such as the Porta Appia (now Porta San Sebastiano) on the Via Appia and the Porta Ostiensis (now Porta San Paolo) on the road to Ostia.

To build quickly and cheaply, the engineers incorporated existing buildings. Stretches of aqueducts, the walls of the Praetorian Guard’s camp, the Amphitheatrum Castrense and many tombs and houses were absorbed into the circuit. The marble Pyramid of Cestius, a tomb of the 1st century BC, became part of the wall beside the Porta Ostiensis. The circuit also crossed the Tiber to enclose part of Trastevere.

The line of the walls followed practical rather than symbolic boundaries. It enclosed an area of nearly 14 square kilometres, including all seven traditional hills and the Campus Martius, but left out some districts where people already lived. A significant part of the circuit’s length was formed by earlier structures, which reduced the cost and time needed. Who did the work is not recorded; the army was busy elsewhere, and the labour probably came largely from the city’s civilian workforce and its guilds.

Purpose and design

The first walls were not designed to withstand a long siege by a major army with siege engines. Their aim was to stop fast-moving raiding bands, which lacked the equipment and time for a siege, and to reassure the city’s population. Even so, building walls around the capital was a striking admission of insecurity, and many other cities of the empire were fortified at the same time. In Gaul, cities such as Paris, Bordeaux and Tours built compact new walls in the late 3rd and early 4th centuries, often reusing stones from earlier monuments and enclosing only a small part of the former town.

The gates were the strongest points. Each was flanked by towers, usually semicircular, and many originally had two arched openings, one for traffic in each direction. Small posterns, or side doors, gave access at other points, and latrines and windows for archers were built into the towers.

Later strengthening

The walls were upgraded several times. Maxentius, who ruled Rome from 306 to 312, began raising them and deepening the ditch in front, although he was defeated by Constantine before the work was complete.

The biggest rebuilding came under the emperor Honorius in 401–403, directed by his general Stilicho, in response to the threat from the Visigoths under Alaric. The walls were roughly doubled in height, the gates were rebuilt with stronger towers, and the Mausoleum of Hadrian across the Tiber was turned into a fortified bridgehead. Inscriptions celebrating this work still survive over several gates.

The walls in history

Despite these improvements, Alaric entered Rome on 24 August 410 through the Porta Salaria, probably because it was opened from within. The Sack of Rome in 410 shocked the Roman world. In 537–538, during the Gothic War, the Byzantine general Belisarius defended the city from behind the walls against a year-long siege by the Ostrogothic king Vitiges.

The walls continued to be repaired by the popes through the Middle Ages and Renaissance, and new bastions were added in the 16th century. The last time they played a military role was on 20 September 1870, when troops of the Kingdom of Italy opened a breach near the Porta Pia and entered the city, ending the temporal rule of the popes over Rome. The date gave its name to Via XX Settembre.

What survives today

About 12.5 kilometres of the original circuit, roughly two-thirds, still stands, making the Aurelian Walls one of the longest and best-preserved city walls of the ancient world. Some sections were demolished in the late 19th and 20th centuries to make way for roads and railways, and many gates have been modified or rebuilt. Several gates, such as Porta del Popolo, were given new Renaissance or Baroque facades, while others were walled up in the Middle Ages and reopened only in modern times. Conservation of the brickwork is a constant task for the city, and partial collapses after heavy rain have occurred in recent decades.

The best-preserved gate is Porta San Sebastiano, which houses the Museum of the Walls, from which visitors can walk along a section of the wall-walk. Other notable points include Porta Maggiore, where the wall incorporated monumental aqueduct arches, and the Pyramid of Cestius beside Porta San Paolo.

By the numbers

Timeline

• 270–271: Juthungi and Alamanni invade northern Italy.
• 271: Aurelian orders the construction of the walls.
• c. 280: The walls are completed under Probus.
• 306–312: Maxentius begins raising the walls.
• 401–403: Honorius and Stilicho rebuild and heighten the circuit.
• 410, 24 August: Alaric’s Visigoths enter Rome through the Porta Salaria.
• 537–538: Belisarius defends Rome against the Ostrogothic siege.
• 1870, 20 September: Italian troops breach the walls near Porta Pia.

Why it matters

The Aurelian Walls mark the moment when Rome, once protected by distant frontiers alone, had to defend itself at home. For more than 1,500 years they shaped the city’s growth, its defence and its image, and they remain one of the largest surviving monuments of the Roman Empire.