The Battle of River had been an important victory for the Muslims. While having only sustained minor casualties, the Muslims had been able to defeat a large Sassanid army and to acquire a vast amount of booty. By now Khalid had organised an efficient network of intelligence agents. The agents were local Arabs who were hostile to the Persians. The agents informed Khalid about the concentration of new Sassanid armies in the area of Walaja and their much greater numbers. Khalid had to get to Hira, and Walaja was directly on his route.