The Story of the Leonine Walls

By Chris Petitt

The urban wall that once enclosed St. Peter’s Basilica and its neighborhood is one of the best-preserved monuments of medieval Rome, but seldom gets the love it deserves. How many who pass through the wall or encounter parts of it in the hotels, restaurants and other buildings constructed along it and that even incorporate it into their design, know when, why and how it was built?

Until the fifteenth century, travelers arriving in Rome via the pilgrimage routes that traversed northern Italy would pass through the Porta San Pellegrino (then 600 years old) and see—if not read—this inscription:


Traveler who comes and goes, notice this beauty that Leo IV has now willingly built. These fair summits shine with shaped marble made by men’s hands and pleasing for their beauty. This triumphant prelate carried out this great work that you see in the time of the unconquered Caesar Lothar. I believe that the wars of evil-mined men will never harm you, nor will your enemies triumph further. Rome, head of the world, splendor, hope, golden Rome, o nurse, behold how your prelate’s effort is on display! This City is called Leonine from its founder’s name.

Look back 600 years. The Liber Pontificalis, the serial biography of early medieval popes tells us that on June 27, 852, Pope Leo IV and his clerical entourage of bishops, priests, deacons and “all the orders of the Roman Church,” barefoot, their heads covered with ashes, consecrated Porta San Pellegrino with this prayer:


O God, who did confer on your apostle Peter the keys of the kingdom of heaven and did grant him the pontificate of binding and loosing, grant that the help of his intercession we may be delivered from the bonds of our sins; and cause that this city which we have newly founded with your assistance may ever remain safe from your wrath and have and manifold triumphs over the enemy on whose account it has been constructed; through our Lord Jesus Christ. 

This blessing of the newly built walls concluded several years of labor instigated by a sacking of St. Peter’s by Muslim buccaneers. The walls would continue to serve some defensive role for hundreds of years.

The Leonine Walls were roughly two miles in length. It ran westward from the Tiber and enclosed St. Peter’s Basilica and the adjacent area, which included churches and monasteries, and the borghi – neighborhoods of foreign residents that developed around St. Peter’s. Though nearly all of the western and southern segments of it have disappeared, several substantial lengths of the northern segment survive in the Vatican gardens and (more visibly) along the street that runs from the Castel Sant’Angelo to the Vatican Palace. To the scholar and to the curious traveler, the wall evokes questions. The story of the wall, the when, the how, and the why, is worth knowing.

A plan of Rome in the Middle Ages. The Leonine City is visible in the upper left section. From Historical Atlas by William R. Shepherd, 1923.

The Assault on St. Peter’s Basilica

The sea off the west coast of Italy had been dominated by Muslim freebooters based in Africa and al-Andalus for much of the ninth century. The life of Pope Sergius II in the Liber Pontificalis provides a patchy account of what happened in Rome. On Monday, August 23, 846, in the pontificate of Sergius, a band of them landed at Ostia (now Ostia Antica), the port of Rome. Contemporary reports state that 11,000 men, 500 horses and 73 ships constituted the raiding force. This force overwhelmed the garrison at Ostia and chased the relief militia sent from Rome, which included Romans as well as Franks, Saxons and Lombards, back to the city and to refuge behind the third-century Aurelian Walls.


The Romans and their friends were safe there behind the imperial-age walls, but the richly endowed cult centers outside of the walls, especially the basilicas of St. Peter and St. Paul, remained vulnerable to plundering by, what a contemporary Roman writer called, “that plague-bearing race.” The raiding party arrived at Rome around twilight on August 25. Having been deterred from entering the city, the invaders turned their attention to the basilica of St. Peter. The motley force in Rome left the city to engage the marauders there at the site of St. Peter’s martyrdom, but their intervention was unsuccessful:

…and there the horseman swarmed from the ships, and made a surprise attack on St. Peter the prince of apostles’ church with unspeakable iniquities. Then all the companies of Romans, left leaderless, came out to Campus Neronis to face the armed men …

This Roman account ends in mid-sentence, apparently due to loss in manuscript preservation, but the choked voice enhances the drama of the moment.


The shock of this blow to the caput mundi meant that accounts spread throughout Christendom, and more monastic chroniclers outside of Rome recorded the immediate effect of this invasion. For example, the Annals of St-Bertin reports that “The Saracens and the Moors laid waste the basilica of St. Peter and, along with the very altar which had been placed over his tomb, they carried off all the ornaments and treasures.” The gift-based endowment of the basilica was an act of piety between celestial patron and earthly clientage. The sacking of St. Peter’s was a symptom of trouble in the relationship.

The Porta San Pellegrino – photo by Lalupa / Wikimedia Commons

No accounting of the treasure lost during the sack of St. Peter’s and other suburban churches, including St. Paul’s on Via Ostiensis, was made, but no itemized bill could measure the shock caused by the violence at the very center of Latin Christendom. The endowment of St. Peter’s by emperors and popes had begun 500 years before this sacking. A sampling of gifts to St. Peter made by contemporary popes recorded in the Liber Pontificalis hints at the scale of the lost munificence. To St. Peter, among other gifts, Pope Gregory IV (d. 844), the predecessor to Sergius, restored to St. Peter the apostle’s church “to its ancient condition and standard what was damaged due to old age”. Pope Paschal I (d. 824) gave “a fine gold image with the face of God’s Holy Mother” weighing 10 pounds, four ounces, a Gospel book with a silver cover weighing eight pounds, eight ounces, and for the adornment of the altar 200 pounds of gold; and Leo III (d. 816), the pope who consecrated Charlemagne Holy Roman Emperor, provided St. Peter with thousands of pounds in silver and gold used in liturgical implements and other adornments, including, for example:

Over the high altar in St. Peter his mentor’s basilica, this venerable pontiff provided a canopy of fine silver gilt, with various representations, beautifully and wondrously decorated on a wondrous scale weighing overall 2,704 pounds and three ounces.

One wonders how it compared to Bernini’s marvelous baldocchino that covers the altar today. Leo IV and other patrons of the basilica had work to do to restore the idea, at least, of what once was in those desecrated sites.


The papal and imperial response

The raiders did not make a clean break with their loot. A combination of fighting with Italian ships and stormy weather wrecked at least part of the bandits’ fleet. Still, the conflict was not yet done. The following year Muslim raiders returned to the coast around Rome with the apparent aim of returning to the city and the endowed churches that stood vulnerable outside its walls, but they were defeated near Ostia. The papal and Frankish imperial authorities now had two objectives. One was to protect the basilica of St. Peter from future incursions by building a wall to protect the shrines and the settlements that had grown up around it, and the other was to replenish the endowment of the basilica.

The Battle of Ostia in 849, painted by Raphael’s assistants, 1514–1515, Stanza dell’Incendio del Borgo, Raphael Rooms, Apostolic Palace, Vatican City – Wikimedia Commons

The papacy and the empire were allies and competitors. The newly elected Pope Leo IV is the better-remembered benefactor of Rome, but the work of Emperor Lothar I and his son and successor Louis II (great-grandson of Charlemagne) in achieving those objectives, especially as fundraisers, was essential to their success. Each man wanted to be perceived as the primary benefactor of the restoration of St. Peter’s Basilica. Contemporary sources were partisan and championed either papal or imperial claims. Frankish material resources were critical to success in Rome, but the popes were the more visible protagonists of the restoration after the sack.

In the fighting around Ostia, the Romans captured a substantial body of Muslim prisoners in the course of these raids. The Liber Pontificalis provides no hard numbers, but stated that the number was so great as to be unmanageable. Consequently, the Romans divided the captives into two groups. The men in one group were executed by hanging, and the trees of Ostia and the road toward Rome were filled with the condemned men. The other prisoners were brought to Rome and made to be forced labor, including work building the wall around St. Peter’s:

We ordered that some should live, bound in iron, but for one reason only so that they could know clearer than light both our hope, which we have in God, and his ineffable piety, and also their own tyranny. After this to stop them living idly or without distress among us, we were bidding them to carry out everything, sometimes at the wall we were building around St. Peter the apostle’s church, sometimes at various manufacturers’ tasks, whatever seemed necessary.

The southern Italian chronicle Chronicon Comitae Capuae covers the end of the story of Muslims around Rome in this period. There was a continued Muslim presence in area south of Rome into the early tenth century, but the city itself was not attacked again. The last redoubt of the invaders was on the river Garigliano, today the boundary between the regions of Lazio and Campania. The fortified camp there was eliminated by the Battle of Garigliano in 915. Allied Roman (led by Pope John X), Frankish, Lombard and Byzantine armies massacred the Muslim fighters, with one commentator stating the Garigliano River “ran red with their blood”.

The Assumption of the Virgin, Pope St. Leo IV at left, detail of a 9th-century fresco in the basilica of S. Clemente, Rome.

The replenished endowment of St. Peter’s Basilica

At the same time that the walls were being built, Pope Leo IV and other donors began to replenish the endowment of St. Peter’s with liturgical furnishings. The contemporary biography of Leo describes the gifts he made to St. Peter. The confessio of St. Peter, the area of the saint’s tomb, received the most conspicuous of these. Together the tomb, altar and confessio comprise the most sacred area of the basilica. A staircase leads down to confessio, which is slightly below floor level. This is the same level as the grottoes of the current basilica, where the tombs of popes continue to be placed. The tombs of the grotto level around the tomb of Peter. This level is slightly raised above the ancient cemetery buried beneath the church, where Peter was first interred. Leo IV’s gifts to confessio and the relics of St. Peter there demonstrate the significance of the place:

In St. Peter the Apostle’s church after the looting this God-protected pontiff provided fine silver railings weighing 800 pounds, which are in front of his confessio; and four silver-gilt panels which are on the steps in the front of the confessio, and two lambs, which together weigh 44 pounds. There too he presented crowns in porphyry of wondrous size, decorated in fine gold with 12 dolphins with an inscription of the name of this bountiful prelate, the actual gold weighing 3.5 pounds, also 10 fine silver arches there decorated around with gold interweave.

Leo also provided gifts for liturgical use in other parts of the basilica all made with precious metals, silk and jewels. The most spectacular may have been “a crucifix constructed of wondrous size of fine silver-gilt and with jacinth jewels and one other large pearl, weighing 77 pounds.” The volume and quality of gifts presented here attest to the importance of this shrine as the spiritual center of Roman Christendom.

Dedication of the walls: June 27, 852

The walls created what early medieval documents call the “new City” and more frequently the Civitas Leonina, the Leonine City, after its founder Pope Leo IV. After performing the blessing and evocation at the Porta San Pellegrino, Pope Leo and his clerical entourage continued on their procession around the circuit of the walls. This movement paused at the two other gates in the wall, where similar evocations were made and inscriptions that lauded the work of Leo were placed.

Then at last with the works of the new city finished and completed as we have related, the blessed pope, who is in all things praiseworthy, in order that this city (which is called Leonine from its founder’s own name) might stand strong and firm forever, order with the devotion of a great spirit and in joy of heart that all the bishops, priests, deacons, and all the orders of the clergy of the Roman church should, after litanies and the chanting of the psalter, with hymns and spiritual chants, go with him round the whole circuit of the walls, barefoot and with ash on their heads. Among other things, he enjoined that the cardinal bishops should bless water so that the office of the prayers they might be zealous in casting that water in every direction to hallow the wall as they cross it. They humbly fulfilled what he had ordered. The venerable pontiff himself pronounced three prayers over this wall, with much weeping and sighing, asking and beseeching that this city might both be preserved forever by Christ’s aid and endure safe and unshaken from every incursion of it enemies by the guardianship of all the saints and angels.

The penitential character of the liturgy was the act of piety made to restore that fracture between the blessed Peter and the Roman Church. The pontifex maximus Leo IV, as his life in the Liber Pontificalis tells us, had repaired “ancient rites and customs of the Church that his predecessors had broken and abolished”.

Chris Petitt (M.Phil.—Medieval History) is preparing an anthology of eyewitness writing about Rome from antiquity to the present day. Contact him at [email protected]