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
Caesar Invests the Camp of Pompeius
As his phlegmatic opponent persevered in his inaction, Caesar undertook to occupy the circle of heights which enclosed the plain on the shore held by Pompeius, with the view of being able at least to arrest the movements of the superior cavalry of the enemy and to operate with more freedom against Dyrrhachium, and if possible to compel his opponent either to battle or to embarkation. Nearly the half of Caesar's troops was detached to the interior; it seemed almost Quixotic to propose with the rest virtually to besiege an army perhaps twice as strong, concentrated in position, and resting on the sea and the fleet.
Yet Caesar's veterans by infinite exertions invested the Pompeian camp with a chain of posts sixteen miles long, and afterwards added, just as before Alesia, to this inner line a second outer one, to protect themselves against attacks from Dyrrhachium and against attempts to turn their position which could so easily be executed with the aid of the fleet. Pompeius attacked more than once portions of these entrenchments with a view to break if possible the enemy's line, but he did not attempt to prevent the investment by a battle; he preferred to construct in his turn a number of entrenchments around his camp, and to connect them with one another by lines. Both sides exerted themselves to push forward their trenches as far as possible, and the earthworks advanced but slowly amidst constant conflicts.
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Reference address : http://www.ellopos.net/elpenor/rome/5-10-brundisium-pharsalus-thapsus.asp?pg=72