Palazzo del Bargello in Florence

You're standing at the Bargello in Florence. Look up along that stern stone façade with its battlements. This is the oldest public building in the city. Construction began in 1255, for the Capitano del Popolo, and from 1261 it was the seat of the podestà, the highest magistrate in Florence. The Palazzo Vecchio was even modelled on it. Look at the top storey: you can tell it by the smaller stone blocks, because it was only added after a fire in 1323. And then there's the 54-metre tower, La Montanina. Its bell was rung to warn the people of Florence when the city was under attack.