The Celtic tribe in the area were named "Icauna", after the River Yonne which they thought sacred. The region was later occupied by Gallic tribes. In that period, the area came under the control of the Roman Empire, whose chief town was Sens, which they called Agendicum. It was the capital of their province of Gallia Lugdunensis, one of four provinces into which France was subdivided. The present main roads from Lyon to Boulogne, and from Sens to Alise-Sainte-Reine date from this period. About this time, Auxerre, Tonnerre (Tornodurum) and Avallon were growing in size. In the fourth century, Sens became a walled city. The first bishops were appointed in Sens and Langres, and they influenced the region profoundly because of their power.