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
According to it, in this year the governor of Macedonia Sextus Pompeius fell near Argos (not far from Stobi on the upper Axius or Vardar) in a battle fought with these Celts; and, after his quaestor Marcus Annius had come up with his troops and in some measure mastered the enemy, these same Celts in connection with Tipas the king of the Maedi (on the upper Strymon) soon made a fresh irruption in still larger masses, and it was with difficulty that the Romans defended themselves against the onset of the barbarians.(13)
13. The quaestor of Macedonia M. Annius P. f., to whom the town of Lete (Aivati four leagues to the north-west of Thessalonica) erected in the year 29 of the province and 636 of the city this memorial stone (Dittenberger, Syll. 247), is not otherwise known; the praetor Sex. Pompeius whose fall is mentioned in it can be no other than the grandfather of the Pompeius with whom Caesar fought and the brother-in- law of the poet Lucilius. The enemy are designated as --Galaton ethnos--. It is brought into prominence that Annius in order to spare the provincials omitted to call out their contingents and repelled the barbarians with the Roman troops alone. To all appearance Macedonia even at that time required a de facto standing Roman garrison.
Things soon assumed so threatening a shape that it became necessary to despatch consular armies to Macedonia.(14)
14. If Quintus Fabius Maximus Eburnus consul in 638 went to Macedonia (C. I. Gr. 1534; Zumpt, Comm. Epigr. ii. 167), he too must have suffered a misfortune there, since Cicero, in Pison. 16, 38, says: -ex (Macedonia) aliquot praetorio imperio, consulari quidem nemo rediit, qui incolumis fuerit, quin triumpharit-; for the triumphal list, which is complete for this epoch, knows only the three Macedonian triumphs of Metellus in 643, of Drusus in 644, and of Minucius in 648.
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Reference address : https://www.ellopos.net/elpenor/rome/4-05-peoples-north.asp?pg=22