With regard to letters and art, the period from 610 to 717 is the darkest epoch in the entire existence of the Empire. After the abundant activity of the preceding century, intellectual creativeness seemed to have died out completely. The main cause of the sterility of this period must be sought in the political conditions of the Empire, which was forced to direct all its energies toward defense against its external enemies. The Persian, and later the Arabian, conquest of the culturally advanced and intellectually productive eastern provinces of Syria, Palestine, Egypt, and North Africa, the Arabian menace to Asia Minor, the islands of the Mediterranean, and even the capital itself, the Avaro-Slavonic menace in the Balkan peninsula all this created conditions practically prohibitive of any intellectual and artistic activity. Unfavorable conditions prevailed, not only in the provinces torn away from the Empire, but also in those which still formed part of it.