"Started in 1155 under the consulate of Coconut Griffi , are the oldest example in Italy of the city walls almost completely preserved. Previously, the city had a late Roman walls, all on the right bank, and a more restricted during the Middle Ages , which cut out many public buildings such as baths , the amphitheater and the harbor , which fell into disrepair and were used as quarries of building material .
Gradually, with the revived importance of Pisa and its maritime trade, developed new neighborhoods with houses, churches and monasteries, especially in the east and northeast, but also in the swampy area west of the river Ozzeri , also on the left bank there was a satellite city, where they settled freely people of every background and religion, working in the garages for caravans, cargo storage areas and in other commercial and manufacturing.
The resolution of the construction of the new walls came at a time of great economic prosperity and proceeded without special urgency being planned from the beginning a time of realization around fifteen to twenty years. Were employed different types of stone, creating still vivid color effects, from white to pink in the lower battlements, with regular drafts and well-squared (a prerogative that has very few similar examples at the time), and he created a fence on both the banks of ' Arno , which included 185 acres of land, with a perimeter of about six miles, an average thickness of two meters and winds and an average height of eleven meters. The walls also defined a new approach to urban planned, with the axis-Via Borgo Ponte Vecchio and the Arno to divide it into four square areas.
The walls rise still some defensive towers (the tower of Santa Maria , the Tower of St. Agnes and the Lion Tower ) and you open the ancient gates.
The walls were restored by the Medici after the occupation of the city in the sixteenth century , with the construction of a citadel that was adapted to the new military techniques of firearms . In the twentieth century some parts of the walls were torn down, for example, close to the station or in the San Paolo a Ripa d'Arno , also some parts were damaged during the Second World War.
Currently the Pisan walls are damaged by smog that causes browning and the spread of numerous climbing plants, such as ivy, which are undermining the stability of the danger of collapse of some parts . Fortunately, starting in January 2012 began a complete restoration of the walls, the redevelopment of the adjacent land and the restoration of walkways made ??possible thanks to funds from the share PIUSS and that will end by 2014 . The restoration has, however, sparked the protest architect Massimo Carmassi complaint that too much invasiveness, and in particular are cited in the stucco mortar white material that is inappropriate for these restorations, partial plugging of the battlements and the visual impact of the railings to protect the walkway. "
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