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In this system, the day began at sunset and ended at the following sunset. Reference to an event at "two hours into the day" meant 2 hours after sunset. Therefore, a date on the Florentine calendar is dated in the present dating system either the same date or the following date, e. g. 10 August on the present calendar is 10 August on the Florentine calendar until sunset, after which 10 August on the present calendar is 11 August on the Florentine calendar until midnight (0:00), after which the dates synchronize to 11 August on both calendars.
The year also began 25 March, the Solemnity of the Annunciation, and not on 1 January. Therefore, the Florentine calendar, along with those of Pisa and the Republic of Siena, belonged to the "stile dell'Annunciazione" o "dell'Incarnazione"("style of the Annunciation" or "of the Incarnation"), in contrast to the calendars of the "stile della Natività" ("style of the Nativity"), which began the year on the Solemnity of the Nativity of the Lord (Christmas) on 25 December, e. g. the calendars of Arezzo, Assisi, and Perugia, in present Italy.
This is the reason that some dates have an apparent discrepancy of one year. For example, a birth date of 10 March 1552 in Florentine reckoning translates to 10 March 1553 in present reckoning, setting aside the aforementioned discrepancy in the beginning of the day. Beginning the year on a date other than 1 January was common during the mediaeval period: the English year also began on 25 March, until 1752; the Venetian year began on 1 March, until the Fall of the Venetian Republic; and the French year on Easter day, until 1564 (see beginning of the year).
Italy was one of the few regions to immediately convert from the Julian calendar to the Gregorian: 4 October 1582 was followed by 15 October 1582, the latter being the first day of the new Gregorian calendar. Not until 1749, however, were the ancient calendars definitively outlawed in Tuscany: in that year the recently appointed Grand Duke and Holy Roman Emperor, Francis I, ordered that, starting from 1750, the first of January should become the first day of the year, thus having the "peoples of Tuscia" conform to all the others. A plaque in Latin commemorating the grand ducal/imperial decree is affixed to the west wall of the Loggia dei Lanzi, in Piazza della Signoria.
- The plaque is reproduced online and translated into Italian at the "FlorencewithGuide" website (Silvia Bonacini, Il calendario fiorentino). Two similar plaques are affixed in Pisa and Siena.