The top line of windows across the Ponte Vecchio hide the Vasari Corridor which is an elevated enclosed passageway connecting the Palazzo Vecchio on the north side of the Arno with the Palazzo Pitti on the south. It was built in five months by order of Duke Cosimo I de' Medici in 1565. The idea of an enclosed passageway was motivated by the Grand Duke's desire to move freely between his residence and the government palace (the Florence Town Hall), when, like most monarchs of the period, he felt insecure in public. The meat market of Ponte Vecchio was moved to avoid its smell reaching into the passage, its place being taken by the goldsmith shops that now occupy the bridge. In its Uffizi section, the Vasari Corridor is used to exhibit the museum's famous collection of self-portraits (https://en.wikipedia.org/wiki/Vasari_Corridor). The corridor can also be seen on the right side of the Arno after it does a right angle turn on exiting the bridge.