The Romans defeated the Macedonians in 168 BC in the Battle of Pydna; the Romans destroyed Corinth in 146 BC, and Athens in 186 BC after a failed rebellion in Asia Minor in which they had aided Mithridates VI, king of the Black Sea region, and the Roman statesman Sulla destroyed the walls of Athens and stole its most precious sculptures. During the next three centuries Greece constituted the Roman province of Achaea, a period of peace known as the ‘Pax Romana’, and the Hellenistic culture of the conquered was absorbed by the conquerors, who had always deeply admired Greek literature, art and philosophy. The period of the Pax Romana ended with invasion of Greece by the Goths.
Christianity became the state religion; St. Paul visited Greece several times in the 1st century AD, and the Roman emporers were among the converts. One of these was Constantine I, emperor of the new capital of the Roman Empire, which had shifted to the city on the Bosporous River which had previously been called Byzantium., this in 324 AD. The new capital was named for Constantine, hence ‘Constantinople’, or City of Constantine (Konstantinoupoli in Greek, which is still what Greeks call this city, known otherwise as Istanbul, in modern times).
Christianity became the official religion of this eastern Roman Empire (Byzantine Empire) in 394 AD, when Emperor Theodosius I outlawed worship of the old Roman and Greek gods, now deemed pagan. In 529 AD, Emperor Justinian banned the teaching of classical philosophy, replacing it with the study of Christian theology. The Byzantine Empire lasted about eleven centuries (4th to 15th centuries AD), its decline accelerated by the Fourth Crusade and the sacking of Constantinople in 1204 AD, a Crusade engineered by the Venetians, who were greedy for the wealth of the imperial city, and which, ironically, pitted Christian against Christian, this despite the stated purpose of the Crusades, which was to free the Holy Land from the Muslims.
After this shameful pillaging of the city, the Empire was divided up into feudal states ruled by Frankish or western Germanic princes, with the Venetians gaining control of all major Greek ports, and their turning islands into Venetian dukedoms, including the island of Crete.
One exception was the Byzantine city of Mystras in the Peloponnese, which became the seat of power for one of the last Byzantine emperors, Palaeologos VIII, and also an intellectual center . This same emperor reclaimed the city of Constantinople in 1261, though it had fallen far from its former glory.