In 52 BC, Julius Caesar's Gallic Wars came to an end, but he refused to return to Rome, despite the Senate's demands that he lay down his arms. Cato personally detested Caesar, and was his greatest enemy in the Senate; Cato's political faction, the Optimates (also known as the Boni), believed that Caesar should return to Rome, in order for the Optimates to strip him of his property and "dignitas", and permanently exile Caesar. In 49 BC, Caesar crossed the Rubicon with his army, thus declaring war, beginning the Great Roman Civil War. Both Cato and Bibulus allied with Gnaeus Pompeius Magnus against Caesar. Though both Boni hated Pompey, he did not pose the threat to their faction that Caesar did. Bibulus commanded Pompey's navy in the Adriatic Sea. He captured a part of Caesar's fleet, although this was generally insignificant as Caesar went on to decisively defeat Pompey at the Battle of Pharsalus. Bibulus died in 48 BC following Pompey's defeat, leaving Porcia a widow.