The Battle of Pharsalus was fought at Pharsalus (Greece) on August 9, 48 BC, between the Populares faction of the Roman Republic, led by Gaius Julius Caesar, and the Optimates faction, led by Gnaeus Pompeius Magnus. The victory of Caesar weakened the Senatorial forces and solidified his control over the Republic.
The date of the battle is given as 9 August. This is according to the republican calendar. The date according to the Julian calendar, was either 29 June 48 BC (according to Le Verrier's chronological reconstruction) or 7 June 48 BC (according to Drumann/Groebe). Pompey was assassinated on September 3rd. The point is not entirely academic; had the battle taken place in the true month of August, when the harvest was becoming ripe, Pompey's strategy of starving Caesar would have been senseless.