For three centuries since the death of Alexander, the Mediterranean had subjected itself to the Hellenistic Age. To the north, Greece itself, cultural hub. To the south, Egypt, dynastic hub, ruled by the descendant of Alexander’s general Ptolemy, Cleopatra.
Into this, the newest and toughest kid on the block was the Republic of Rome. Julius Caesar had been assassinated, his heir Octavius ruled the west and hellophile Mark Antony the east. Cleopatra had borne Julius’s child and with Mark Antony produced more.
By the Battle of Actium in 31BC, Octavius wrought the end of the Hellenistic Age and secured the commencement of his own age with the murders of Julius’s son and Mark Antony’s son and heir.
Octavius himself entered Alexandria on 1 August 30BC with Mark Antony committing suicide the same day.
On the face of things, Octavius was bringing Egypt into the republic but and of course he was soon become and is better known to history as Augustus the first of the Roman emperors.
Five centuries on, and things had somewhat backflipped. The western empire had come and gone, although the eastern empire, which we usually call the Byzantine empire, was still operating. Its greatest emperor was probably Justinian, who took office on 1 August AD527. He was one of the last emperors to be able to lay claim to Egypt.