Republican Calendar

http://www.historyofwar.org/articles/concepts_republican_calendar.html

During the Napoleonic wars most of Europe used the Gregorian calendar with the exception of Russia, which used the Julian calendar until the revolution of 1917. Between 1792 and 1805 France used what was known as the Republican Calendar. In this all the months were renamed and years began with the foundation of the Republic at An I. All months had 30 days except the 12th month, which had 35 or 36 on a leap year. The Republican year ran from September to August.

Months

Vendemiaire	22 September-21 October
Brumaire	22 August-20 November
Frimaire	21 November-20 December
Nivose	21 December- 19 January
Pluviose	20 January-18 February
Ventose	19 February-20 March
Germinal	21 March-19 April
Floreal	20 April-19 May
Prairial	20 May-18 June
Messidor	19 June-18 July
Thermidor	19 July-17 August
Fructidor	18 August-21 September

Years

1792-3	I
1793-4	II
1794-5	III
1795-6	IV
1796-7	V
1797-8	VI
1798-9	VII
1799-1800	VIII
1800-01	IX
1801-2	X
1802-3	XI
1803-4	XII
1804-5	XII
1805	XIV