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
Battle near Beneventum-- Pyrrhus Leaves Italy-- Death of Pyrrhus
The king took the field in the spring of 479 with the view of aiding
the hard-pressed Samnites, in whose territory the Romans had passed
the previous winter; and he forced the consul Manius Curius to give
battle near Beneventum on the -campus Arusinus-, before he could
form a junction with his colleague advancing from Lucania.
But the
division of the army, which was intended to take the Romans in flank,
lost its way during its night march in the woods, and failed to appear
at the decisive moment; and after a hot conflict the elephants again
decided the battle, but decided it this time in favour of the Romans,
for, thrown into confusion by the archers who were stationed to
protect the camp, they attacked their own people. The victors
occupied the camp; there fell into their hands 1300 prisoners and four
elephants--the first that were seen in Rome--besides an immense spoil,
from the proceeds of which the aqueduct, which conveyed the water of
the Anio from Tibur to Rome, was subsequently built.