Pisa’s walls are the oldest city walls in Italy that remain almost entirely intact. Construction began in 1154 in the area that corresponds to today’s piazza dei Miracoli, while the seventh and final lot was built in 1161; this section defended the western side of the city, stretching from the Portello to the Torre dell''Arno. The site was chosen strategically, as these ramparts were meant to protect the cathedral and future baptistery and defend the city’s most vulnerable spot: the bridge crossing the Auser River in the northwestern part of Pisa.