On 4 January 48 BCE, Caesar moved seven legions – most likely below half-strength – onto a small fleet he assembled and crossed the Adriatic. Caesar's opponent in the consulship of 59 BCE, Marcus Calpurnius Bibulus, was in charge of defending the Adriatic for the Pompeians: Caesar's decision to sail, however, surprised Bibulus' fleet. Caesar landed at Paeleste, on the Epirot coast, without opposition or interdiction. However, the news of the landing spread and Bibulus' fleet quickly mobilised to prevent any further ships from crossing, placing Caesar at a significant numerical disadvantage.

After Caesar's landing, he embarked on a night march against the town of Oricum. His army forced the surrender of the town without a fight; the Pompeian legate in command there – Lucius Manlius Torquatus – was forced by the townspeople to abandon his position.

Bibulus' blockade meant that Caesar was unable to request food from Italy; and although the calendar reported January, the season was late autumn, meaning Caesar would have to wait many months to forage. While some grain ships were present at Oricum, they escaped before Caesar's forces could capture them. He then moved on Apollonia and forced its surrender, before decamping to attack Pompey's main supply centre at Dyrrhachium.

Pompey's reconnaissance was able to detect Caesar's movement toward Dyrrhachium and beat him to the vital supply centre. With Pompey's substantial forces arrayed against him, Caesar withdrew to his already-captured settlements. Caesar called for reinforcements under Mark Antony to transit the Adriatic to support him, but they were interdicted by Bibulus' mobilised fleet; in despair, Caesar attempted to transit from Epirus back to Italy, but was forced back by a winter storm. Pompey's forces, meanwhile, pursued a strategy of starving Caesar's legions out.

However, Antony was able to force a crossing around the time Bibulus died, arriving to Epirus on 10 April with four additional legions. Antony was lucky to escape the Pompeian fleet with minimal losses; Pompey was unable to prevent Antony's reinforcements from joining with Caesar.