The siege of Pelusium (early 47 BC) was an early victory for Mithridates of Pergamum during his expedition to rescue Caesar, who was then besieged in Alexandria. (Great Roman Civil War)
Soon after arriving in Alexandria, Caesar realised that he might need more troops. Mithridates, who was one of his closest allies, was sent to raise an army in Syria and Cilicia. He was quickly able to raise a sizable force, which he then led towards the Egyptian frontier.
Achillas, the first commander of the Alexandrian army, soon discovered that Mithridates was on his way. He sent a strong garrison to hold Pelusium, the fortress that defended the eastern approaches to the Nile Delta, in the hope that they would be able to stop Mithridates.
Mithridates realised that time was of the essence, and decided to launch an immediate assault on Pelusium. He kept committing fresh troops to the battle to replace those who were getting tired, and managed to capture the fortress in a single day. This was an impressive achievement, as Pelusium had managed to hold out for some time on previous occasions.
After seizing Pelusium, Mithridates resumed his march to Alexandria. Ptolemy XIII, who had now taken command of the Alexandrian army, sent a force to try and stop him, but without success. He then decided to lead a second army in person. Caesar followed, and managed to reach Mithridates before Ptolemy. The resulting battle of the Nile ended as a clear Roman victory. Ptolemy was killed while attempting to escape, and Caesar was free to place Cleopatra on the throne, before returning to the Roman world to resume his civil war.