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
As Caesar was not to be overcome from the landward side, the exertions of the besiegers were directed to destroy his fleet and cut him off from the sea by which supplies reached him. The island with the lighthouse and the mole by which this was connected with the mainland divided the harbour into a western and an eastern half, which were in communication with each other through two arched openings in the mole. Caesar commanded the island and the east harbour, while the mole and the west harbour were in possession of the citizens; and, as the Alexandrian fleet was burnt, his vessels sailed in and out without hindrance.
The Alexandrians, after having vainly attempted to introduce fire-ships from the western into the eastern harbour, equipped with the remnant of their arsenal a small squadron and with this blocked up the way of Caesar's vessels, when these were towing in a fleet of transports with a legion that had arrived from Asia Minor; but the excellent Rhodian mariners of Caesar mastered the enemy. Not long afterwards, however, the citizens captured the lighthouse- island,(42) and from that point totally closed the narrow and rocky mouth of the east harbour for larger ships; so that Caesar's fleet was compelled to take its station in the open roads before the east harbour, and his communication with the sea hung only on a weak thread.
42. The loss of the lighthouse-island must have fallen out, where there is now a chasm (B. A. 12), for the island was in fact at first in Caesar's power (B. C. iii. 12; B. A. 8). The mole, must have been constantly in the power of the enemy, for Caesar held intercourse with the island only by ships.
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Reference address : https://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=104