Ancient Gaul was transformed during the reign of Augustus (r. 31 BC–14 AD) through a major programme of city building. The new Roman cities were constructed according to topographic, health and ritual considerations, and we hypothesise that their orientations also reflect distinct celestial conceptions held by the Gauls and by the Roman emperor Augustus. Our study of the orientation of 60 cities verifies the existence of coherent patterns, and distinguishes two dominant schemes: a pattern prevailing in the south and focused on cardinal orientations, possibly related to the dies natalis of Augustus; and a pattern dominant in the north, focused on the dates of the festivities at the beginning of the seasons from the Celtic tradition. We argue that the orientation of the cities was used by the Gallic elites to express the validity of their cultural tradition when they became a part of the Roman Empire.