When did Byzantium flourish?

The heyday of Byzantium is associated with the reign of Emperor Justinian in the middle of the 6th century, from 527 to 565. In those years, it was the only empire in Europe and one of the four most developed states of the 6th century, on a par with Sassanian Iran, India and China.
Justinian controlled the entire northern coast of Africa, from Sinai to Morocco, the south of modern Spain, almost the entire territory of modern Italy, including Sardinia and Sicily, the Balkan Peninsula, the peninsula of Asia Minor and the entire eastern coast of the Mediterranean Sea and most of the Black coast.