Hirtius, Aulus (ôˈləs hûrˈshēəs) [key], d. 43 B.C., Roman soldier. He was a friend of Julius Caesar, with whom he served in Gaul. After Caesar's assassination (44 B.C.) Hirtius and Caius Vibius Pansa were consuls and took sides with the senate against Antony, who was at Mutina (Modena) besieging Decimus Junius Brutus. Hirtius was killed in the successful lifting of the siege. He was probably the author of the eighth book of Caesar's Gallic Wars. He may also have been the author of Bellum Alexandrinum, a work that continues Caesar's commentary on the civil war.