Pompeius learned through one of Caesar's peace envoys as to his preparations for the voyage to the Epirot coast, and, thereupon accelerating his march, threw himself just at the right time into that important arsenal.
The situation of Caesar was critical.

Although he extended his range in Epirus as far as with his slight strength was at all possible, the subsistence of his army remained difficult and precarious, while the enemy, in possession of the magazines of Dyrrhachium and masters of the sea, had abundance of everything.

With his army presumably little above 20,000 strong he could not offer battle to that of Pompeius at least twice as numerous, but had to deem himself fortunate that Pompeius went methodically to work and, instead of immediately forcing a battle, took up his winter quarters between Dyrrhachium and Apollonia on the right bank of the Apsus, facing Caesar on the left, in order that after the arrival of the legions from Pergamus in the spring he might annihilate the enemy with an irresistibly superior force.

Thus months passed.
If the arrival of the better season, which brought to the enemy a strong additional force and the free use of his fleet, found Caesar still in the same position, he was to all appearance lost, with his weak band wedged in among the rocks of Epirus between the immense fleet and the three times superior land army of the enemy; and already the winter was drawing to a close.

His sole hope still depended on the transport fleet; that it should steal or fight its way through the blockade was hardly to be hoped for; but after the first voluntary foolhardiness this second venture was enjoined by necessity.