Their territory lay between their neighbors to the northeast, the Sequani, who occupied the Doubs river valley, and the Arverni in the Massif Central. Caesar does not say what the cause of the conflict was, but the Sequani controlled access to the Rhine river along the valley of the Doubs. To that end, they had gradually built up an "oppidum", or fortified town, at Vesontio. Tradesmen headed up the Rhone and its tributary the Saône (the ancient Arar) could not pass the Doubs at Vesontio without coming to terms with the Sequani, and no one could pass from the Rhine to the Rhone but on similar terms. The east of the entire great channel is bordered by the Jura mountains and the west by the Massif Central. Vesontio is from that stretch of the Rhine between Mulhouse and Basel. The Arar formed part of the border between the Aedui and the Sequani. Strabo, who lived a generation after Caesar in the late republic and early empire, does make a statement concerning the cause of the conflict between the Sequani and Aedui, and it was in fact commercial, at least in Strabo's view. Each tribe claimed the Arar and the transportation tolls from traffic along it, "but now", says Strabo, "everything is to the Romans." The Sequani also habitually supported the Germans in their previous frequent expeditions across the river, which shows that Ariovistus's subsequent devastation of Sequani lands represented a new policy. The location of the final battle between the Aedui and their enemies, which Caesar names as the Battle of Magetobriga, remains unknown, but Ariovistus's 15,000 men turned the tide, and the Aedui became tributary to the Sequani. Cicero writes in 60 BC of a defeat sustained by the Aedui, perhaps in reference to this battle. Ariovistus seized a third of the Aeduan territory, settling 120,000 Germans there. To avoid infringing on his allies for the moment, Ariovistus must have passed over the low divide between the Rhine and the Doubs in the vicinity of Belfort and then have approached the Aedui along the Ognon river valley. That move left the Sequani between him and the Jura mountains, not a tolerable situation for either if they were not going to be allies.