Medieval Florence was enclosed in curtain walls that contained today’s historical center. In the last century, restructuring brought the city to be the capital of the Kingdom of Italy and the city walls were demolished, with the exclusion of the gates.
The entire line on the right bank of the Arno was replaced with the actual Avenues of circumrotation. 
The part of city situated on the left bank of the river Arno, called ‘Oltrarno’, still has notable traces of the city walls. Today the goal of restructuring will bring the reopening of some lines of the watch walk, from which it will be possible to enjoy a new vision of the historical beauties of the city. The construction of the city walls began on the 2nd of January 1285 , to replace the first fortified line (1173-1175 ) since the city had expanded beyond the old walls. The new enclosure measured 8500 meters, was endowed of 73 towers and 15 gates and contained a surface of 430 hectares, equal to 5 times that of the previous walls.
The greatness of the work was necessary to face the huge demographic and city expansion.
It’s calculated that in the 1125 Florence counted 25.000 inhabitants, in 1280 came to 80.000 and already grazed 100.000 in the first years of the 14th century. This building entourage was planned to be one of the largest, most powerful and most heavily defended of the time. In fact they became one of the most formidable city walls of medieval Europe. These walls at many places were endowed with a ditch fed by the waters of the Mugnone, a small tributary of the Arno, whose waters raced had been diverted for that purpose. Construction was not finished until 1333 because wars interrupted the work several times. The ‘Magister Murorum‘ (Architects) responsible for designing the walls included Arnolfo di Cambio, Giotto and Andrea Pisano.
Courtesy of Castelli Toscani – Dotflorence Network
