This chapter demonstrates that all of the available evidence indicates that the Notitia system was rapidly put into place in the 440s, likely in response to the invasions of Attila the Hun on the Danubian border. Although designed to face down the threat of the Huns, the system continued to operate as the collapse of Attila’s kingdom put increasing pressure on the eastern empire, in particular in the form of Theoderic Strabo and Theoderic the Amal, two Gothic warlords who repeatedly ravaged the Balkans and assaulted Constantinople during this period. Placed in its proper context, many central features of the Notitia system become intelligible, in particular its strong Balkan focus and the function of the praesental armies, which were used as reserve forces.