Napoleon on the 18th Brumaire by François Bouchot
The 18th Brumaire
was the date of the coup d'etat
when Napoleon seized power in France. The date comes from the French Republican Calendar, which was implemented after the French Revolution in an attempt to rationalise the calendar. It was in use from 1793 to 1805, when Napoleon abolished it. The month of Brumaire started around the 22nd of October; the date of Napoleon's coup corresponds to 9th November 1799 in the ordinary Gregorian calendar.
To confuse matters a little further, Russia at this time worked from the old Julian calendar, which meant that from 1800-1900 it was running twelve days behind the rest of Europe (a fact many historians have taken to be more than a little symbolic of the state of the country). The Gregorian calendar was only adopted in Russia after the October Revolution in 1914.