Strabo Geography 4.6.11

[11] One of the passages over the mountains from Italy into Transalpine and northern Keltica is that which passes through the country of the Salassi, and leads to Lugdunum. ¹ This [route] is divided into two ways, one practicable for carriages, but longer, which crosses the country of the Centrones, the other steep and narrow, but shorter; this crosses the Pennine [Alps]. Lugdunum is situated in the midst of the country, serving as an Acropolis, both on account of the confluence of the rivers, and of its being equally near to all parts. It was on this account that Agrippa cut all the roads from this [as a centre] one running through the mountains of the Cevennes to the Santones ² and Aquitaine, ³ another towards the Rhine; a third towards the ocean by the country of the Bellovaci ⁴ and Ambiani, ⁵ and a fourth towards the Narbonnaise and the coast of Marseilles. ⁶ The traveller, also, leaving Lugdunum and the country above on his left, may pass over the Pennine Alps themselves, the Rhone, or Lake Leman, into the plains of the Helvetii, whence there is a passage through Mount Jura into the country of the Sequani, and Lingones; here the road separates into two routes, one running to the Rhine, and the other ⁷ to the ocean.