In the mid-9th century, Europe was divided between the Christian West, the Muslim South and the pagan North and East. Western Christendom was centered on the Carolingian Empire, the surviving Christian kingdoms of northern Iberia and Britain and Ireland. After Charlemagne’s death, Francia was overrun by Vikings like Ragnar Lothbrok whose sons Ivar the Boneless, Halfdan and Ubba invaded Anglo-Saxon England with the Great Heathen Army.
Björn Ironside is more famous for being the first Viking to lead a large fleet into the Mediterranean where he raided al-Andalus, Francia, Italy and the Byzantine Empire. In al-Andalus, the Vikings more than met their match where they went up against the Mamluks and heavy warships called dromons that were equipped with catapults armed with Greek Fire.