Gaius Cassius Longinus (Classical Latin: [ˈgaː.i.ʊs ˈkas.si.ʊs ˈlɔŋ.gɪ.nʊs]; October 3, before 85 BC – October 3, 42 BC) was a Roman senator, a leading instigator of the plot to kill Julius Caesar, and the brother in-law of Marcus Junius Brutus. He commanded troops with Brutus during the Battle of Philippi against the combined forces of Mark Antony and Octavian, Caesar's former supporters, and committed suicide after being defeated by Mark Antony.