One of my favorite episodes from the Anglo-Saxon period of British history is this coin struck in the name of King Offa of Mercia (r. 757–796 C.E.):
Most literate Mercians could easily recognize the English/Latin phrase “OFFA REX” on one side but the rest would have been a mystery. The coin is an imitation of a 774 C.E. Abbasid dinar, including the (incorrectly-copied) phrase “There is no god but God”. The minter would almost certainly have had no idea what the text meant.
One of the implications of the coin is that despite their large cultural gap the commercial gap between the Christian and Islamic regions was much narrower. It’s very well known that Christian Europeans learned a lot, culturally, from Muslim trading partners. The classic example from a few centuries later is Arabic numerals (which likely ultimately originated in India). It is hypothesized that Offa intended this coin to be used in foreign trade rather than in England. Muslim traders were preeminent in the Mediterranean at this time and southern European merchants would have been very familiar with the dinar this coin mimicked.
One of the lessons I try to impart to my students is that commerce is a much bigger part of history than they’ve been taught before. Not only did it expose people to foreign material goods, but it enriched their cultures in the process. The average man on the street seems only to begrudgingly appreciate commerce, but to think of any culture as it stands today without recognizing its foreign antecedents transmitted because of commerce is a great historical misunderstanding.
UPDATE 2105/03/15: Via Twitter, there are more examples from other parts of Europe.