The defeat remained unavenged, for it was realized that the pursuit of the Basques in their mountain fastnesses was impossible. This expedition into Spain not only accomplished little in the way of permanent conquest, but served to provoke the Moslems to successful reprisals extending over a series of years in the Southern part of Gaul. The country was harried by the invaders, and towns as important as Carcassonne and Narbonne were attacked and the country about them ravaged. Dissensions among the Moslems themselves brought a respite, and, aided by insurgents against the authority of the Cordovan Caliphate, the Frankish officers in Aquitaine later on extended the sphere of Frankish influence far into the Iberian peninsula. Before the end of Charles’ reign Navarre and Pampeluna were again occupied, and he could number Barcelona among the cities of his empire. After the conquest of Bavaria, the campaign against the Avars, a people closely allied to the Huns, was brought about by their threatening attitude on the Eastern frontier, where they showed such constant hostility to the peoples of German stock that in his military handling of the problem Charles had the ready coöperation of the Saxons themselves. After a preliminary campaign in 791, in which the Franks advanced as far as the confluence of the Danube and the Raab, the decisive struggle took place in 795, when the Frankish army, under Pippin, the son of Charles, taking advantage of dissensions among the Avars, succeeded in forcing the famous armed camp of the Khan called the Ring, and returned with an immense amount of booty stored there, the fruits of many successful raids on Christian towns and monasteries. In 809 the Avars, hard-pressed by the Slavs, were glad to place themselves under the Emperor, but their number had been so reduced by warfare that a contemporary historian speaks of their lands as being deserted, their treasures confiscated, and their nobility wiped out. Operations against the Slavic tribes were taken up in earnest after the reduction of the Saxons, though we hear of one marauding expedition against them as early as 789. In 805 and 806 Slavic territory was overrun by Frankish armies under the command of the Emperor’s lieutenants, and two strong outposts were established for purposes of military observation of their movements. These posts, on the Saale and on the Elbe, became the nucleus for the development of the German cities of Halle and Magdeburg.