Augusta Treverorum, as the chief city of the province of Gallia Belgica, rises in importance from 271 to 274 during the Empire's major third-century crisis.

Trier is the second city of the breakaway Gallic Empire, at first under Postumus, who was proclaimed in Cologne, then under his ephemeral successor, Victorinus, who made his base at Trier, where he had rebuilt a large house with a mosaic proclaiming his position as tribune in Postumus' Gallic Praetorian Guard; the city serves again as capital under the emperors Tetricus I and II.

Internal conspiracies and extensive incursions by Germanic tribes, together with the increasingly extreme severe monetary inflation that obtains during the third century and now reaches a peak, have prevented the Gallic empire from achieving stability.

Tetricus, having elevated his son, also Tetricus, to the rank of caesar (junior emperor), continues to be threatened by successive mutinies.

Aurelian in late 273 leads an army across the Alps and marches north into Gaul.