When Justinian died on
November 14, 565, Justin was elevated to the imperial throne. In the first few days of his reign he paid his uncle's debts, administered justice in person, and proclaimed universal religious toleration. Contrary to his uncle, Justin relied completely on the support of the aristocratic party.
In
568 the
Lombards invaded
Italy under
Alboin, and in a few years they made themselves masters of nearly the entire country. Justin's attention, however, was distracted from Italy towards the North and East frontiers. Proud of character, he discontinued Justinian's policy of buying off potential enemies. After refusing to pay tribute to the
Avars, Justin fought several unsuccessful campaigns against them, therefore he was forced to pay them 80,000
silver pieces. More importantly, in
572 his refusal to pay tribute to the
Persians in combination with overtures to the Turks led to a war with the Sassanid Empire. After two disastrous campaigns, in which the Persians overran
Syria and captured the strategically important fortress of
Dara, Justin reportedly lost his mind. The temporary fits of insanity into which he fell warned him to name a colleague. Passing over his own relatives, he raised, on the advice of Sophia, the general
Tiberius to be Caesar in December
574 and withdrew into retirement. In 574, Sophia paid 45,000
nomismata to Chosroes in return for a year's truce. Sophia and Tiberius ruled together as joint regents for four years, while Justin sank into growing
insanity. When he died in
578 Tiberius succeeded him as
Tiberius II Constantine.