Why do historians consider the greatest achievement of the Byzantine Empire to be the preservation of Greek and Roman cultures?

Answer 1

The Byzantine Empire is often called the "preserver" of Greco Roman Heritage, because it was influenced so heavily by Greek and Roman culture. The official language of the Byzantine Empire was Greek and the government was strongly based off of Roman Law. The Byzantine Empire also used Greek and Roman culture to influence the creation of its Church and its magnificent Art & Architecture. By using all these Greco Roman values and parts of society, the Byzantine Empire was able to "preserve" Greek and Roman heritage.

Answer 2

The Byzantine Empire was the continuation of the Roman Empire. This is a term which has been coined by historians to indicate the eastern part of the Roman Empire after the fall of the western part of this empire. The west fell under the strain of the invasions by the Germanic peoples. The east was not affected by these invasions and continued to exist for nearly 1,000 years. The people in question did not know this term and called their empire Roman Empire.