The need for a fortification, preventing access to Rome through its south-west side, derived from a conflict between two noble Roman families, the Barberini (the house of the Pontiff) and the Farnese, due to economic interests and to the policy of expansion of the former against the latter.

In the summer of 1641 the Pope himself, leading an army of 15,000 men with artilleries, marched against the Duchy, occupying its territory and the town of Castro: in effect, the economic interests concealed political matters, as well as a kind of feud between rival families, and Urban was waiting for nothing but a pretext to set off the spark.

Despite the fears of Urban, the wall had to face no serious threat for two centuries, until in 1849 it became one of the main scenes of the fights between the French army of the General Oudinot (helping the Pope, who was about to lose the temporal power over the city) and the militias of the 2nd Roman Republic.

After a battle lasted the whole day, with continuous turn-arounds and a very high death toll on both sides, the Frenchmen gained the upper hand, but the walls held up and the defenders didn't cede.

The area of Porta Portese, just a few meters from the present Ponte Sublicio, is the lowest of the whole layout: the rise to the Janiculum hill begins soon beyond, partly due to the raising of the ground level.

After a short stretch north-westward, the wall makes a right angle southwest and goes on in a non-linear way flanking Viale delle Mura Portuensi up to Largo Bernardino da Feltre, just where probably it crossed the ancient Aurelian layout.

Furthermore, the entire stretch of wall from here up to Porta San Pancrazio is a sequence of signs, more or less visible, of restorations (patchings, traces of subsidences and collapses), that evidently lasted at least until 1861, according to the just mentioned plate of Pope Pius IX.

The stretch, starting soon after the two modern arches on Via Fratelli Bonnet allowing the viability, is the one most damaged by the military events of 1848, commemorated by two plates newly restored, placed just where a sizeable breach was opened.

The following downhill stretch shows completely different characteristics, as regards both history (it has suffered no damages from bombings and assaults) and landscape (the quite steep slope didn't allow a building growth in the close vicinity).