In 574, Justin had a mental breakdown, forcing Empress Sophia to turn to Tiberius to manage the empire, which was fighting the Persians to the east and dealing with the internal crisis of the plague. To achieve a measure of breathing space, Tiberius and Sophia agreed to a one-year truce with the Persians, at the cost of 45,000 nomismata. On 7 December 574, Justin, in one of his more lucid moments, had Tiberius proclaimed Caesar and adopted him as his own son. Tiberius added the name Constantine to his own. Although his position was now official, he was still subordinate to Justin. Sophia was determined to remain in power and kept Tiberius tightly controlled until Justin died, in 578.