After peace had been settled with the Persians in the East in 591, Byzantine emperor Maurice and his generals were able to drive back the Slavs and the Avars in a series of campaigns. However, Maurice's victories ultimately failed to restore the stability of the Danube "limes" due to the rebellion of the Danube army in 602, which led to Maurice's deposition and murder, and the accession of the usurper Phocas. The renewal of war with Persia meant the rapid and complete collapse of the Danube frontier in the first decades of the 7th century, as imperial forces were withdrawn to the East. Phocas and his successor Heraclius bought off peace with the Avars through annual tributes, but the Slavs once again had a free hand in raiding the Balkans, and in 604, a force of 5,000 men suddenly attacked Thessalonica at night, but failed to scale the city walls.