'wrapped' a 200 m section of the Aurelian Wall in Rome, by the Pincian Hill Gate.
Although the Walls were built by Aurelius, the Pinciana Gate in its current form dates to the reign of Honorius (395-423). In 401 he realised that the Barbarians would soon be at the Gates, and ordered improvements to Rome's fortifications.
Rome's main walls during the Republic were the Servian Walls. Although they were modified and improved repeatedly into the late Republic, their origins are thought to date from the reign of Servius Tullius. The walls were certainly greatly rebuilt following the Battle of Allia, when the Gauls sacked the city (390 BC). The surviving wall is made using stone from Veii, which as not conquered until 393 BC, providing a terminus post quem.
The city of Rome grew, and the population during the Empire outgrew the walls. Whilst the Pax Romana held, this was not an issue.
The Third Century AD was one of troubles, with a secession of weak emperors - it took six to bring down Zenobia and her army, although she was a 'mere' woman. Just as she had tried to carve out her own empire in the East, so the Vandals, successors of the sacking Gauls, descended from the North to do the same.
Aurelian - as well as finally defeating Zenobia - initiated a massive construction project to wall the city of Rome and provide her with strong defenses against invaders. The Aurelian walls were begun in AD 271, and completed soon after his death in 275. Aurelius Victor includes them in this rather odd list of Aurelius' achievements, which does not include the reconquest of Palmyra and Egypt [De Caesaribus, 35.5-6]:
That man first introduced among the Romans a diadem for the head, and he used gems and gold on every item of clothing to a degree almost unknown to Roman custom.Structures standing in the way were built into the walls, one of the greatest architectural projects the city had seen since the time of Hadrian. The Vandals tended to raid rather than besiege, as did the other Goths of the period. For a while the Walls continued to protect Rome.
He fortified the city with stronger, more solid walls. For the populace, he instituted a ration of pork.
Honorius improved them, and incorporated Hadrian's Tomb into them as a fortress. In time the tomb became the Castel Sant'Angelo, used for its near impregnability by the popes - Clement VII hid in it during the Sack of 1527.
Honorius' walls proved to be no deterrent to Alaric, who sacked Rome in 410 - see Procopius for the details. This was the first sack of the city since the Gauls, but would be followed by many more. Geiseric's Vandals sacked Rome again in 455. Totila's Ostrogoths in 546 and again in 549; they also .
The Saracens did not spare Rome in 846, looting St. Peter's and San Paolo fuori le Mura, both outside the walls. To prevent a repeat raid, Leo IV ordered that the area around the Vatican be walled too. Henry IV of Germany and the Normans still sacked the city again in 1084.
This engraving by Piranesi shows the Pyramid of Cestius built into the Aurelian Walls. The setting is rather dramatically over-exaggerated, as the walls were not in such poor condition in the 18th century - many other engravings show them near complete at the time. The Aurelian walls and gates continued to be used during the many sieges - and subsequent falls - of Rome, until the 19th century.
Parts of the Servian Walls are also still visible, notably near the Termini Station, and on the Aventine Hill (with a particularly interesting section used as a base for a catapult, which dates to the Civil Wars).
A sketch from Christo's 1973 project is coming up at auction in London:
The Wall (Project for a Wrapped Roman Wall/Porta Pinciana, delle mura aureliane - Via Vittorio Veneto and Villa Borghese) by Christo (b. 1935) - Christie's London
Museo delle Mura - their web site lists the museum as planning a new display.
A section of the Aurelian Wall crumbled at the end of October 2007.