By the late Empire, enemy forces in both the East and West were "sufficiently mobile and sufficiently strong to pierce [the Roman] defensive perimeter on any selected axis of penetration";[REF] from the 3rd century onwards, both Germanic tribes and Persian armies pierced the frontiers of the Roman Empire [REF].
Larger groups of barbari began to settle in Rome's territories around this time, and the troops they were contracted to provide to the Roman army were no longer organised as numeri but rather were the forerunners of the later rented native armies known as federated troops (Latin: foederati).[REF]