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
Battle at Cannae
While these preparations for the next campaign were being made in Rome, the war had already recommenced in Apulia. As soon as the season allowed him to leave his winter quarters, Hannibal, determining as usual the course of the war and assuming the offensive, set out from Gerunium in a southerly direction, and marching past Luceria crossed the Aufidus and took the citadel of Cannae (between Canosa and Barletta) which commanded the plain of Canusium, and had hitherto served the Romans as their chief magazine.
The Roman army which, since Fabius had conformably to the constitution resigned his dictatorship in the middle of autumn, was now commanded by Gnaeus Servilius and Marcus Regulus, first as consuls then as proconsuls, had been unable to avert a loss which they could not but feel. On military as well as on political grounds, it became more than ever necessary to arrest the progress of Hannibal by a pitched battle. With definite orders to this effect from the senate, accordingly, the two new commanders-in-chief, Paullus and Varro, arrived in Apulia in the beginning of the summer of 538.
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Reference address : https://www.ellopos.net/elpenor/rome/3-05-war-hannibal-cannae.asp?pg=32