Palazzo Senatorio in the 14th century
Built in the XII century on the remains of the ancient Tabularium and utilising pre-existing fortifications built by powerful baronial families, this palazzo makes up the background to the piazza. It owes its name to its function as senatorial seat responsible for the administration of justice.
In 1299 an open loggia was added overlooking the piazza, although this was walled in a century later in order to strengthen the Palazzo, which was turned into a fortress with the addition of towers by Pope Boniface IX; more corner towers were later added by Popes Martin V and Nicholas V.
Michelangelo also designed a monumental double-flighted staircase for the Palazzo Senatorio, in addition to dividing up the façade with gigantic pilaster strips, large windows and tympanums and a crowning balustrade featuring statues.
The work was completed after his death by Giacomo della Porta, who made some alterations to Michelangelo's plan. The bell-tower was also the result of an alteration to the original plan, this time by Martino Longhi the Elder.