The reign of Justinian I saw a revival of the Byzantine Empire as he attempted to restore it to its former glory. Disputes with the Persian Sassanid Empire proved a constant threat to the security of the Byzantine frontier. Justinian signed a peace treaty with Sassanid King Khosrau I in 532, which lasted until 540 and allowed him to focus on conquests in the west. In 533 Justinian invaded the Vandal Kingdom in North Africa and set about removing any trace of Vandal authority and the Arian Church in the region. Special priority was placed on recapturing the old Roman heartland of Italy, which was now territory of the Ostrogoths. After a lengthy campaign, Italy was secured in 554 and the Byzantines enjoyed naval superiority throughout the Mediterranean, holding almost the entire coastline. Although Justinian had regained much of the territory of the old Roman Empire, it came at a huge financial cost.
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