The Eastern Roman emperor Justinian took this as a pretext to interfere Hindering in Vandal affairs , and after he secured Preventing_or_letting his eastern frontier with Sassanid Persia in 532 , he began Process_start preparing GetReady an expedition under general Belisarius , whose secretary Procopius wrote Writing the main historical narrative of the war .

In 615 , during the ongoing war with the Byzantine Empire , the Sassanid Persian army under spahbod Shahin invaded Attack Asia Minor and reached Arriving Chalcedon , across the Bosporus from Constantinople .