In 1443, Paolo Uccello – a Tuscan painter and mosaic artist who played a major role in Florence’s 15th-century art scene – painted the face of the clock on the counter-façade of the Florence Cathedral, Santa Maria del Fiore. He included four heads colored in fresco at the corners, as Vasari wrote, whose identity is still the object of debate amongst critics.

The huge clock’s hand moves counter-clockwise according to the so-called “hora italica”, which divides the day into twenty-four equal parts throughout the year and associates the beginning of the day with sunset (“ab occasu solis”). It is the same system used by the Clock Tower in Piazza San Marco in Venice and by the astronomic clock in Prague: invented in the 1300s, it used to be convenient to determine how many hours of light were left in the day (since hours were counted from sunset on, all you had to do was subtract the time displayed from twenty-four).