Starting from the beginning of 12th century this walls were no longer sufficient. The extra-walls villages became greater and crowded, they took name from the churches or monasteries that rose at their extremities: Borgo San Lorenzo, along the via Cassia toward the great Ambrosian Basilica; Borgo di Balla toward the countryside of Cafaggio; Borgo di San Remigio, at east to the church with this name; Borgo di San Piero (along the today Borgo degli Albizi) to the monastery of S.Pier Maggiore; Borgo di Campo Corbolini to west. Also across the Arno rose many villages.
All this caused great military and logistic problems. When the ‘Comune’ of Florence conquered this districts was planned a new defensive enclosure to include the new suburbs and to prevent the feudal punitive expeditions. At the time the war between City States and Feudal Power reached its aim, due to the descent in Italy of the emperor Frederick Barbarossa.In 1170 was decreed the construction of the new town walls, in 1172 started the works that ended in 1175. The course of this fifth enclosure is easily recognizable on every map of the city, all the outside villages are now encircled, the walls took a rough triangular shape. From Castello d’Altafonte the enclosure took the western direction, far from the Arno banks in order to let more space to the river port, which communicate with the city through a little gate. To north-east the walls followed Via de’ Benci until Porta S.Pietro (nowadays Borgo degli Albizi), here turned north-west along Via S.Egidio until Canto de’ Nelli where it turned south through Via del Giglio and Via della Croce al Trebbio down to the present day Ponte alla Carraia. The southern side ran along the river but was also started the fortification of the other (left) bank of the Arno (of which we will talk in separate part).
This new enclosure was for the time quite perfect, whit great free green space, especially near the main gates, ready to be quickly urbanized. The old walls were sold to be used as base for other constructions of as quarry for new buildings. In the old center, inside the disappeared Roman walls, the lack of free spaces started the vertical development of the Tower-Houses. But all this was not enough: during the 13th century the city grew more and more, out of all expectations. A large immigrant movement, the deviation of the Via Francigena to east that put Florence again on the main road toward Rome, were the main causes of the great urban development of the city.
At the beginning of 13th century Florence counts about 50.000 inhabitants, that become 75.000 at the half and about 100.000 at the end of the century. Again, villages, hamlets (like Borgo Porta Faenza, Borgo Pinti, Borgo la Croce, Borgo Ognissanti and many more), monasteries and settlements of the mendicant orders (for examples the Franciscans of Santa Croce and the Dominicans of Santa Maria Novella) grew outside the gates and along the main roads: things had returned to the previous state! The defence, and hygienic, problems required the introduction, for the first time in a medieval city state, of a policy of urban planning. Many illegal buildings were build against the city walls. A new enclosure was necessary.