 Upon the start of the civil war, Marcellus fled Rome with the "optimates" and joined the Republican Grand Army in Epirus.After the Battle of Pharsalus, Marcellus abandoned opposition to Caesar, and withdrew in an honorable exile to Mytilene, where he was left unmolested by Caesar.His cousin Gaius Claudius Marcellus petitioned the dictator for clemency, as did Cicero in his "Pro Marcello".