 Complete the following phrase:  Aurelians construction of the walls as an emergency measure was a reaction to the barbarian invasion of 270; the historian Aurelius Victor states explicitly that the project aimed to alleviate the citys vulnerability. It may also have been intended to send a political signal as a statement that Aurelian trusted that the people of Rome would remain loyal, as well as serving as a public declaration of the emperors firm hold on power. The construction of the walls was by far the largest building project that had taken place in Rome for many decades, and their construction was a concrete statement of the continued strength of Rome. The construction project was unusually left to the citizens themselves to complete as Aurelian could not afford to spare a single legionary for the project. The root of this unorthodox practice was the imminent barbarian threat coupled with the wavering strength of the military as a whole due to being subject to years of bloody civil war, famine and the 