Final answer:
Octavian and Marcus Agrippa captured the city of Alexandria in 30 BCE following their victory in the Battle of Actium.
Step-by-step explanation:
Octavian, who later became known as Augustus, and Marcus Agrippa captured the city of Alexandria in 30 BCE. This military action occurred in the aftermath of the Battle of Actium, where Octavian's fleet, commanded by Agrippa, defeated the forces of Marc Antony and Cleopatra. Following their defeat at Actium, Antony and Cleopatra fled back to Egypt, where Octavian and Agrippa eventually invaded, leading to the surrender of Alexandria, Antony and Cleopatra's demise, and the incorporation of Egypt into the Roman Empire.