According to tradition, the city of Rome was founded in 753 BC. (Archaeology suggests that people lived at that location far earlier, but likely for most or all that time, they did not consider themselves “Romans.”) The last Roman king was deposed in 509 BC, creating the Republic of Rome, which expanded over the centuries to rule the Mediterranean basin. Under Octavian Caesar, called Augustus, the Republic was replaced by the Roman Empire in 27 BC. This Empire continued to be ruled from Rome until Emperor Constantine moved the government to Constantinople in 330 AD. Constantine thus began the Byzantine Empire, which was viewed as a continuation of Roman government and culture; this Empire survived until the fall of Constantinople to the Ottoman Turks in 1453 AD.
In other words, the duration of the Byzantine Empire from Constantine until the Ottoman success was more than eleven centuries, a few more years than those that encompass the entire traditional Roman history from the founding of the city to the moving of the government. Given continuity of Roman culture, the Roman civilization lasted more two thousand years. Even treating the Byzantine Empire as a separate entity from Rome, its existence for eleven centuries makes it far more durable than most other Empires and other centralized governments of human history.
When historians focus attention upon the immigration of Germanic groups into the western Empire and neglect the continuity of Roman civilization in the eastern Empire, they misinterpret history. The west blended Roman civilization, law, and traditions with their Germanic ways; the east became more Greek in its outlook, but remained as a major world power through dozens of emperors. The Byzantine Empire had challenges of its own from immigrants, including Goths and Bulgars and Slavs and Avars. Later, it protected Europe from the advance of Islamic civilization, although it lost north Africa and parts of western Asia in the process. Roman literature, science, architecture, and philosophy were preserved by the Byzantines, as was the Christian religion. All of these were them communicated with other civilizations. Missionaries from Constantinople brought Christianity north into eastern Europe, even inventing an alphabet so they could share the Gospel of Jesus Christ with the Russians. Meanwhile, the Byzantine Empire remained a key link in the Silk Roads which united the continents in an economic system of trade (along with transportation of technology and of ideas) over the centuries. The Byzantine Empire was essential for world civilizations and particularly for the continuing development of western civilization while it remained in power.
The Emperor Justinian, two centuries after Constantine, was one of the most important rulers of the Byzantine Empire. He recodified Roman Law, enabling it to survive into modern times and to shape the legal codes of many current governments. He strengthened Byzantine power in the Mediterranean Sea, even recapturing some of the lands that had been claimed by Germanic governments. He also shared political power with his wife, Theodora—much to the dismay of many men in the eastern government and Church. Justinian, like Roman emperors before him, supported the arts and was responsible for beautification of the capitol city—in his case, including the construction of the church building called Hagia Sophia, or Holy Wisdom.
In the eleventh century, Muslim military forces in western Asia were strengthened by the influx of Turks from central Asia, who had been displaced by the growth of China. Needing reinforcements to keep his borders secure, the Byzantine Emperor called for help from European Christianity. Thus began the Crusades. The Emperor was not impressed with the quality of warrior arriving from the west, but he prepared to place them as shock troops in front of his better-trained soldiers. Instead, they headed south and captured Jerusalem, establishing five western-style kingdoms in the Holy Land, kingdoms that lasted more than a century. The eventual decline of those kingdoms led to further crusades, including the disastrous Fourth Crusade, which sacked Constantinople and never made it to Jerusalem. This event, though eventually overturned by Byzantine fighters, was the beginning of the end of the Byzantine Empire, even though it held on for another two centuries after that catastrophe. Distrust between eastern Christianity and western Christianity had begun before the Crusades and only worsened during these times. The fall of Constantinople was not recognized in Europe for the turning point of history that it became, although not many more years would pass before Turkish warriors were at the gates of Vienna, threatening to overwhelm western civilization. But that story awaits another chapter. J.