The clock on the counter façade of the cathedral often gets overlooked as, once inside, we immediately make our way towards the high altar. But this is one of my favourite things in here. It dates to 1443, was frescoed by Paolo Uccello and still tells the time correctly today, give or take a few minutes. In order to be able to tell the time, however, we need to know exactly how they told the time back then, at least on the Italian peninsula. They followed the hora italica or Julian time, as they had done in the Roman Empire, after the changes made by Julius Caesar to the calendar and time calculation. This was a 24 hour system with the day finishing at sunset and restarting as darkness set in, just as seeds grow first in the darkness of the soil, and the clock arm works its way through the hours counter clockwise, imitating the shadow of a sundial. It is adjusted about every two weeks, taking into account the changes in the length of the days. The French began to organise the time into 12 hours, starting from midnight, as we do today, and how the ancient Greeks had done, and this began to be slowly adopted in Italy from the 1580’s, after the adjustments to the Julian calendar under Pope Gregory XIII, with the Gregorian calendar. The Florentines changed the time system in 1750.