What are the most important achievements of Byzantium in the early Middle Ages?

The Byzantine Empire remained intact after the raids of the Franks, unlike Rome. It has preserved many cultural traditions of destroyed Rome and antiquity. Also, the Byzantine Empire became the main center of literacy and science, because various scientific knowledge developed in it. There were many written sources in Byzantium. Scientists made discoveries in the field of mathematics, physics, astronomy. The Byzantines had their own language in which chronicles were written. Architectural styles became widespread.