At its peak, the Byzantine Empire covered vast swathes of Eastern Europe as well as much of North Africa and the Mediterranean coast. By the time that Constantine IV came to power, however, the empire was in decline once more. And the rich lands of Syria and Egypt were in enemy hands, too.
For half a century, Arab forces had been slowly encroaching on the provinces held by the Byzantine Empire. But Constantine took measures to halt their expansion, and he successfully defended the city of Istanbul – then known as Constantinople – against a half-decade siege.
Constantine also helped end the ongoing controversy surrounding the Church, settling the debate that had been raging between different Christian doctrines. Yet it should be noted that his reign was not exactly a peaceful one. In fact, it’s claimed that Constantine ordered both of his brothers be mutilated – a practice that would have rendered them unable to reign as emperors.