Gregorian calendar It also specifies its epact relative to 1 January, in contrast with the Julian calendar, which specified it relative to 22 March. The old date was derived from the Greek system: the earlier "Supputatio Romana" specified it relative to 1 January. During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it was often necessary to indicate the date of some event in both the Julian calendar and in the Gregorian calendar, for example, "10/21 February 1750/51", where the dual year accounts for some countries already beginning their
Adoption of the Gregorian calendar Austerlitz was the confusion between the Russians, who were using the Julian calendar, and the Austrians, who were using the Gregorian calendar, over the date that their forces should combine. However, this tale is not supported in a contemporary account from a major-general of the Austrian Imperial and Royal Army, who tells of a joint advance of the Russian and Austrian forces (in which he himself took part) five days before the battle, and it is explicitly rejected in Goetz's 2005 book-length study of the battle. The date when each country adopted the Gregorian calendar, or an equivalent, is marked