The Walls of Rome

James Tice and Allan Ceen
Department of Architecture, Pennsylvania State University
Department of Architecture, University of Oregon

The wall circuits of Rome provide a frame of reference for the city both as a measure of its growth and prosperity and also as a testament to the vicissitudes of a great city, its image of itself and the practical needs for security during times of travail and even during times of peace.

Earliest Walls

The wall circuits of Rome (recinto) can be thought of as roughly concentric in nature, emanating out from the city’s pre-historic core at, or near, the ancient Roman Forum. The encircling hills and enfolding valleys helped to define these human lines of demarcation whereby natural rifts in the landscape were exploited to establish lines of defense.

The Republican Wall Circuit

The oldest wall circuit is a matter of conjecture but certainly would have encircled the city’s earliest settlements which would include the Capitoline and Palatine hills.

The Servian walls were erected by Servius Tullius, a 6th century B.C. king, who ruled Rome well before the Republic. In his time some defense work was built, probably a ditch and stockade or wall, known as the Agger in the modern train station area to the northeast where there was no natural barrier. Using some of Servius' circuit, the Republican walls were built after the Gallic invasion of 390 B.C.. This wall circuit stretches across the Tiber and encompasses the city’s famous seven hills: Capitoline, Quirinal, Viminal, Esquiline, Celian, Aventine and Palatine. It grew in response to political, religious and residential centers but was tempered by topography which again was exploited to provide for natural lines of defense. Three of the original seven hills of Rome were free standing (Palatine, Aventine, Capitoline) while the remaining four are spurs of a plateau, which is why the Agger noted above continued to serve as a defensive trench, to separate them from the rest of the level countryside east of the city.

The city’s public and religious institutions locate within this circuit and were served by a sophisticated infrastructure of aqueducts and consular roads. These regional arteries pierced the walls at strategic locations that provided check points, customs houses and related practical and honorific functions.

Vasi's Porta del Popolo

Aurelian Wall Circuit

Rome soon outgrew the Republican walls and became so powerful a force in Italy and the Mediterranean that it felt no need for city walls until the late 4th century A.D. when the Barbarian pressure from the east began to threaten the empire. By the time of the late Empire the city had grown to the enormous size of over one million inhabitants.
The city had spilled over into the Campus Martius within the fold of the Tiber and generally moved outward from the epicenter of the forum. The area of the city tripled in the process.

Boundaries for the wall were established as before by taking the natural topography into account. Whenever possible earlier built features were incorporated into the circuit such as the Acqua Marcia and Acqua Claudia aqueducts. Even the famous pyramid tomb of Caius Cestius which as a place of burial, as we know, would originally have been outside the Republican walls, became an ersatz feature in the new defensive circuit.

Later Wall Circuits

With the splitting of the Empire by Constantine into an Eastern and Western half in the 4th century A.D., coupled with the ravages of Barbarian attacks from the 5th century on, the city shrank to an area well within the Aurelian walls, largely abandoning the seven hills with the populace shifting to the low lying areas near the Tiber because the cutting of the aqueducts deprived them of the only other source of water.

Consequently the city center relocated in the Campus Martius where river and well water were available. While the medieval city shrank to a population of little over 10,000, an expansion of the walls by Leo IV (847-855) to include St Peter's resulted in the creation of the only really defensible part of Rome called Borgo or the Leonine City, anchored by Castel S.Angelo (a fortified transformation of the 2nd century Tomb of Hadrian) on the east and St. Peter’s basilica on the west. At the beginning of the 15th century the city's population was a mere 20,000. Compared to other urban centers such as Florence, Milan or Naples, Rome was a sleepy backwater whose pretensions of being "caput mundi" had faded ignominiously into moldering ruins, broken infrastructure and uninhabited fields.

Vasi's Porta San Paolo

In the Renaissance the Popes moved their residence to Borgo from the indefensible Lateran area. Nicolas V (1447-1455) expanded the Borgo walls to include the Vatican hill; Paul III (1534-1549) converted them into bastioned walls capable of resisting cannon fire; Pius IV (1559-1565) doubled the urban area of Borgo and enclosed this area with a wall anchored on the newly bastioned Castel S. Angelo. Urban VIII (1623-1644) linked the Borgo with Trastevere by building a bastioned wall along the ridge of the Gianiculum hill. Paul III's ambitious project to shorten the Aurelian wall and to convert it into a bastioned circuit was short-lived: only two short sections of this were built, one between Porta Appia and Porta Ostiense, and one on the Aventine hill.