The Franks became foederati in 358, when Emperor Julian let them keep the areas in northern Roman Gaul, which had been depopulated during the preceding century. Roman soldiers defended the Rhine and had major armies south and west of the Rhine. Frankish settlers were established in the areas north and east of the Romans and helped the Roman defence by providing intelligence and a buffer state. The breach of the Rhine borders in the frozen winter of 406 and 407 ended the Roman presence along the Rhine when both the Romans and the allied Franks were overrun by a massive tribal migration of Vandals and Alans.