Between the 3rd and 5th centuries hordes, chiefly of German descent but also of other races, moved from the northern and eastern parts of Europe towards territories of the Roman Empire. Following the natural routes alongside the rivers Evros, Strymon, and Axios or the military routes across the mountains, hordes of Huns repeatedly pillaged Thrace and Macedonia. In the 5th century Ostrogoths swept across Macedonia (where they laid siege to Thessalonike) and, like the Huns, reached as far south as Thermopylae.
To oppose these barbarian incursions the Byzantine Empire employed administrative ruses as well as their military forces. Typical of the former was the conclusion of a particular kind of agreement ('foedus') which provided for an alliance with barbarian bands in exchange for economic grants and the right of settlement in imperial lands.