Within the borders of the Rhine River and the Alps, a Germanic confederation, the Alamanni, who occupied a good part of the Agri Decumates (the territory located between the mouth of the Rhine and the Danube), crossed the Alpine steps and attacked the fertile plain of the Po River. The sacking of the area instilled fear in the city of Rome, the empire's capital, as it had yet to become a walled city. The Senate of Rome hastily organized a contingency of plebs for combat in an attempt to ensure that the shrinking army was capable of protecting the city.