Many historians regard him [Offa] as the most powerful....

“ Many historians regard him [Offa] as the most powerful Anglo-Saxon king before Alfred the Great. In the 780s he extended his power over most of Southern England. One of the most remarkable extantfrom King Offa's reign is a gold coin that is kept in the British Museum. On one side, it carries the inscription Offa Rex (Offa the King). But, turn it over and you are in for a surprise, for in badly copied Arabic are the words La Illaha Illa Allah ('There is no god but Allah alone'). This coin is a copy of an Abbasid dinarfrom the reign of Al-Mansur, dating to 773, and was most probably used by Anglo-Saxon traders. It would have been known even in Anglo-Saxon England that Islamic gold dinars were the most important coinage in the world at that time and Offa's coin looked enough like the original that it would have been readily accepted abroad. ”

Jim Al-Khalili