Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Arrival of Caesar
When Caesar following the track of Pompeius arrived in the roadstead of Alexandria, all was already over. With deep agitation he turned away when the murderer brought to his ship the head of the man, who had been his son-in-law and for long years his colleague in rule, and to get whom alive into his power he had come to Egypt. The dagger of the rash assassin precluded an answer to the question, how Caesar would have dealt with the captive Pompeius; but, while the humane sympathy, which still found a place in the great soul of Caesar side by side with ambition, enjoined that he should spare his former friend, his interest also required that he should annihilate Pompeius otherwise than by the executioner.
Pompeius had been for twenty years the acknowledged ruler of Rome; a dominion so deeply rooted does not perish with the ruler's death. The death of Pompeius did not break up the Pompeians, but gave to them instead of an aged, incapable, and worn-out chief in his sons Gnaeus and Sextus two leaders, both of whom were young and active and the second was a man of decided capacity. To the newly-founded hereditary monarchy hereditary pretendership attached itself at once like a parasite, and it was very doubtful whether by this change of persons Caesar did not lose more than he gained.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=99