WALLS

The first architectural defenses of Rome were constructed by the legendary founder of the city, Romulus, who fortified the Palatine hill. These works probably consisted of nothing more elaborate than a simple wooden palisade augmenting the steep natural walls of the hill itself. Both the Palatine and the Capitoline hills would have served as natural fortresses for the inhabitants of the city.

The oldest known comprehensive circuit of walls was attributed to the sixth king of Rome, Servius Tullius, and thus were known as the Servian Walls. Servius Tullius had divided the city into four regions, and his walls were said to surround these four regions. The Servian circuit of walls enclosed the central portion of the city near the Tiber, including the Capitoline, Palatine, and Aventine hills, and also extended inland, encompassing the spurs of the Quirinal, Viminal, Esquiline, and Caelian hills. It did not include the Campus Martius or the Transtiberim, and the eastern edge cut rather awkwardly across the middle of the parallel lines of hills on that side of the city. While Servius Tullius may have erected some sort of fortifications, the walls that bear his name are actually believed to have been constructed several centuries later, in the fourth century bc, as a response to the Gallic sack of Rome in 390 bc.

Standard Roman fortifications consisted of an embankment of earth known as an agger with a ditch in front of it known as a fossa. This was the defense put around Roman legionary camps on the march, and a similar structure may have been built around Rome at an early stage. The stone walls of Servius ran for 11 kilometers and at sections were 10 meters high and 4 meters thick. They were composed of rectangular blocks of cut stone that are consistently 2 Roman feet high (0.6 meters), although the length of the blocks varied. The blocks seem to have been laid atop one another dry, without the use of mortar. The Servian Walls are known to have been rebuilt and augmented on a number of occasions, most notably at times when the city was in peril due to warfare in Italy—for example, in 217 bc during the Second Punic War and in 87 bc during the Social War. These later rebuildings introduced some modifications, including the addition of mountings on the walls for ballistae (a form of catapult).

Although by the early first century ad, the built-up part of the city extended considerably beyond the old Servian Walls, a new circuit of walls to encompass the whole city was not constructed for several centuries. This clearly reflects the security that the Romans felt that no enemy threatened the heart of the empire and illustrates the dominance and stability of Rome during this period, so they felt it unnecessary to bother fortifying their capital city.

This situation changed dramatically in the third century ad, when barbarian incursions grew more serious and the empire was racked by civil wars that often saw rival Roman armies fighting for control of the capital. These events prompted the emperor Aurelian to construct a new, larger circuit of walls in the 270s ad. These walls, known as the Muri Aureliani, were 19 kilometers long and included the Campus Martius and a section of the Transtiberim, as well as stretching farther to the south and east than the Servian Walls. The walls were 6.5 meters high and 4 meters thick, with towers placed every 100 Roman feet. They had a concrete core with brick facing. The towers were equipped with emplacements for two ballistae on swivels as well as numerous loopholes for archers. The gateways were heavily fortified with towers as well, with the main entrances flanked by large, semicircular towers.

The Aurelian Walls show evidence of having been constructed in haste. For example, they make considerable use of existing structures, which are incorporated into the circuit of the walls, including the walls of the camp of the Praetorian Guard, houses, and even stretches of aqueducts. It has been estimated that nearly one-sixth of the walls is actually composed of preexisting structures. These walls also were rebuilt and augmented on numerous occasions. Some of the most important of these additions were made by the emperor Maxentius in ad 311 in preparation for his fight with Constantine. He may have doubled the height of sections of the wall, adding additional stories to the watchtowers. Other rebuildings included those undertaken by the emperors Honorius and Theodoric, and Pope Leo incorporated the Vatican within the circuit of walls.

The walls continued to be maintained and rebuilt throughout the Middle Ages, and the Renaissance popes likewise put effort into refurbishing these fortifications so that they could continue to protect Rome for centuries after the Roman Empire. Today, considerable stretches of the Aure-lian Wall are still visible and quite well preserved, particularly around a number of the gates, among them the Porta Metrovia, the Porta Appia, and the Porta Aurelia on the Janiculum hill.