Despite the Umayyads' success at establishing a more or less stable frontier anchored at Derbent, they were unable to push any further, despite repeated efforts, in the face of vigorous Khazar resistance. Dunlop drew parallels between the Umayyad–Khazar confrontation at the Caucasus and that between the Umayyads and the Franks at roughly the same time across the Pyrenees that ended in the Battle of Tours, noting that, like the Franks in the west, the Khazars played a crucial role in stemming the tide of the early Muslim conquests. According to Peter B. Golden, during the long conflict the Arabs "had been able to maintain their hold over much of Transcaucasia", but notes that despite occasional Khazar raids, this "had never really been seriously threatened. On the other hand, in their failure to push the border north of Derbent, the Arabs were clearly "reaching the outer limits of their imperial drive".