Under Justinian I, the Byzantines recaptured territory in North Africa, Italy and Spain. For a time, it seemed that the Byzantines were capable of recapturing the full territory of the old Roman Empire.
Justinian's experienced generals defeated the Vandals and Ostrogoths, Germanic tribes that had carved up much of the Western Roman empire. However, the lengthy Italian campaign against the Ostrogoths proved to be incredibly costly. This contributed to the fact that Byzantine territory would shrink for centuries after Justinian's death. Later in history, the Byzantines would temporarily win back territory but were never able to stop their overarching territorial decline.