 Almost no Mercian coins are known from the 830s , after Wiglaf regained Mercia from Egbert of Wessex . Beorhtwulf restarted a Mercian coinage early in his reign , and the extended gap in the 830s has led to the suggestion that Wiglaf 's second reign was as a client king of Egbert 's , without permission to mint his own coinage . Beorhtwulf 's coinage would then indicate his independence of Mercia . However , it is more usually thought that Wiglaf took Mercia back by force . An alternative explanation for Beorhtwulf 's revival of the coinage is that it was part of a plan for economic regeneration in the face of the Viking attacks . The Viking threat may also account for the evident cooperation in matters of currency between Mercia and Wessex which began in Beorhtwulf 's reign and lasted until the end of the independent Mercian kingdom on the death of King Ceolwulf II in the years around 880 . 
