 Complete the following phrase:  According to the 6th-century historian Procopius, there existed two cities with the name Thannourios. The Byzantine emperor Justinian I  decided to fortify Thannuris, but the first such attempt failed, as the Byzantine army under Belisarius was defeated by the Sassanid Persians. Eventually Justinians efforts were successful, and the town became a truly formidable fortress, to protect the region from Saracen raids. Nevertheless, the Persians captured the fortress 