Completing his governorship, Bibulus returned to the west in 49 BC to find that civil war had erupted between Caesar and Pompey. Aligning himself with Pompey, he was placed in charge of Pompey's fleet in the Adriatic, to ensure that Caesar and his troops could not cross from Brundisium in Italy to Epirus to challenge Pompey's army. Having only assembled half the necessary ships, Caesar decided to take seven legions across the Adriatic, and to have the ships return and transport the remaining legions once they arrived at Brindisi. Transporting seven legions across the Adriatic Sea to Greece would ordinarily be difficult due to the winter season. But because Caesar knew that the calendar was out of step with the astronomical seasons due to his responsibilities as pontifex maximus, he had the advantage of knowing the crossing would be easier than expected. This assisted Caesar to an extent as the Adriatic was sufficiently treacherous to deter Bibulus' war galleys from venturing far from their base at Corfu.