As insanity invaded the mind of Justin, he became aware that he had to name a colleague for succession of his throne. Passing over his own relatives, he raised, on the advice of his wife Sophia, the general Tiberius to be Caesar in December 7 574, adopting him as his son, and withdrew into retirement.
According to John of Ephesus, as Justin II slipped into the madness of his final days he was pulled through the palace on a wheeled throne, biting attendants as he passed. He reportedly ordered organ music to be played constantly throughout the palace in an attempt to soothe his frenzied mind. The tardy knowledge of his own impotence determined him to lay down the weight of the diadem; he showed some symptoms of a discerning and even magnanimous spirit when he addressed his assembly,
You behold the ensigns of supreme power. You are about to receive them, not from my hand, but from the hand of God. Honor them, and from them you will derive honor. Respect the empress your mother: you are now her son; before, you were her servant. Delight not in blood; abstain from revenge; avoid those actions by which I have incurred the public hatred; and consult the experience, rather than the example, of your predecessor. As a man, I have sinned; as a sinner, even in this life, I have been severely punished: but these servants (and he pointed to his ministers), who have abused my confidence, and inflamed my passions, will appear with me before the tribunal of Christ. I have been dazzled by the splendor of the diadem: be thou wise and modest; remember what you have been, remember what you are. You see around us your slaves, and your children: with the authority, assume the tenderness, of a parent. Love your people like yourself; cultivate the affections, maintain the discipline, of the army; protect the fortunes of the rich, relieve the necessities of the poor.
Tiberius received the diadem on his knees; and Justin, who in his abdication appeared most worthy to reign, addressed the new monarch in the following words: “If you consent, I live; if you command, I die: may the God of heaven and earth infuse into your heart whatever I have neglected or forgotten.”
Empress Sophia had therefore to turn to Tiberius to manage the empire, as Tiberius fought Persians to the east and dealing with the internal crisis of a plague. To achieve a measure of breathing space, Tiberius and Sophia agreed to a one-year truce with the Persians. Sophia was determined to remain in power and kept Tiberius tightly controlled until Justin´s death in 578.
The day after his appointment as Caesar, the plague abated, giving Tiberius more freedom of movement than Justin was able to achieve. Tiberius also charted a very different course from his predecessor, and proceeded to spend the money which Justin had doggedly saved in order to defend the imperial frontiers and win over the populace who had turned against Justin.
Alongside generous donations, he also proceeded to reduce state revenue by removing taxes on wine and bread instituted by Justinian I. He also negotiated a truce with the Avars, paying them 80,000 nomismata per year, for which the Avars agreed to defend the Danube frontier, thereby allowing Tiberius to transfer troops across to the east for a planned renewal of the conflict against the Persians.
On 26 September 578 Tiberius was made Augustus by the rapidly failing Justin. Sophia, Justin’s widow, tried to maintain her power and influence by marrying the new emperor Tiberius, but he refused her proposal because he was already married to Ino. When Tiberius had first been raised to the rank of Caesar, Sophia had refused the request for Ino and her children to move into the Imperial palace with her husband, forcing them to reside in a small residence nearby and prohibiting them from entering the palace. Once Tiberius was elevated to the rank of Augustus, however, he had his family moved into the palace and renamed Ino as Anastasia, much to Sophia’s great resentment.