Around the same time, Christianity began to take on and ascended to become Empire’s predominant religion. St Paul came in Greece to proclaim Christianity with his famous “sermon on an Unknown God” in 51 A.D. In 305 AD, Constantine became Emperor of Rome. In 324 A.D., the Emperor Constantine I transferred the capital of the Empire from Rome to Byzantium which took the name of Constantinople.
In 364 AD, the Empire was officially split: the Roman Empire was divided in two parts: the Roman Empire at the west and the Byzantine Empire at the east. The Roman Empire started to decline leaving preeminence to its much wealthier part, the newly-created Byzantine Empire. The strategic location of Constantinople, between the Black Sea and the Aegean, allowed significant control over Eastern and Western half’s of the Roman empire.
Although Constantine blessed Christianity, paganism continued to exist. Christianity started to take a material form with a particular architecture, religions, mosaics and even hymns and theological tracts. Further differences began to take place in religious practices that would influence Greece and the Greek Islands. The Eastern Empire would be and remain principally an Orthodox Country while the Catholic tradition would predominate in the west. Although originally one faith, the two would formally split later on. At that time Greece was, and remains to this day, traditionally Orthodox, with approximately ninety-eight percent of her citizens professing to be Greek Orthodox.
The strength and power in the Roman Empire continued its transition of power to the Eastern Empire in Constantinople. The west faced numerous invaders and was divided in several kingdoms and the power of the Roman Empire moved definitely to the East. Rome was ultimately sacked for the first time in 410 AD. Its decline led to the overall decline in the west and is credited with the beginning of the Dark Ages.
While in the east during the 6th century, the Byzantine Emperor Justinian expanded the empire’s territory by conquering the southern Levant, northern Africa and parts of Italy. He successfully created a centralized bureaucracy and a new fiscal system. However, it was beset by plague that caused many untimely deaths and suffering and hampered the expansion of the Byzantine Empire.
However, the Byzantine Empire was engaged in several wars that had left it very vulnerable. Serious threats came both from the East and West. The more serious threat came from the Islamic civilization that started to expand rapidly. The Islamic forces conquered Egypt, Syria, Iraq, Iran, and Afghanistan. Even Constantinople almost felt under the hands of the Muslims. During the 6th and 7th, Slavic tribes also invaded the Balkans, but the Greek language remained the official language, and Orthodox Christianity, its dominant faith.
During the 9th Century, the Byzantine Empire was ruled by a Macedonian dynasty which expanded the Empire by conquering Antioch, Syria, Georgia, Armenia, Crete and the Greek Islands in the Aegean Sea. This led to the reopening of trade lines. These military successes ultimately improved the economic conditions of the Byzantine Empire. As is usually the case with history, this short period of prosperity was followed by a period of decline. In the 11th century AD, parts of Greece were invaded by a Norman army. A further setback occurred when Turks from Central Asia successfully captured Romanus IV, the first ruler after the decline of the Macedonian dynasty of the Byzantine Empire.
During the later stages of the Byzantine Empire, Greece was divided in several kingdoms ruled by Western princes. Venice started gaining control of many parts of Greece. Many architectural remains of various European rulers, like the Venetians and the Franks can still be seen in many parts of Greece, particularly the Greek Islands.