The clock above the main door inside the Cathedral of Santa Maria del Fiore, or the Duomo, as it is better known in Florence, is the only one of its kind in working order anywhere in the world. To the modern eye, it looks positively bizarre. At its centre, a golden star decorates the blue disc of the clock’s face, whilst the heads of what are believed to be the four evangelists, Matthew, Mark, Luke and John, are encircled at each corner of the dial’s square frame. The clock has only one hand, running anti-clockwise from the Roman numeral XXIIII at the bottom, which does not indicate midnight. The clock, in fact, registers the ora italica (‘Italian time’), also known as Bohemian time or Julian time, after Julius Caesar’s 46 CE calendar, which began at sunset and ended at sunset. In the cathedral, the clock’s main purpose was probably liturgical, marking the hour when vespers, the sunset prayer service, began. Also, in the medieval world so dependent on farming, sunset heralded the end of the long working day that began with the first rays of light. Sunset, however, changes throughout the year, which means, even today, the Duomo’s clock must be reset weekly.