Why did aspects of byzantine civilization continue to spread even as the byzantine empire declined?

Despite the decline of the Byzantine Empire, aspects of the civilization continued to spread due to the influence of Justinian I. The Byzantine Empire refers to the part of the Roman Empire that remained in existence after the fall of the Roman Empire. During his reign as emperor, Justinian reclaimed much of the land that had been previously taken from the Roman Empire. He also created the Justinian Code, which stated that the emperor was the authority who would create and control all laws. Even when the Byzantine Empire declined, these changes to the world remained.