But a contradiction of the claim that you made?

    Common knowledge would have it that slavery did not exist in medieval Europe.

    However, there is a thriving body of scholarship which demonstrates that slavery was practiced widely in various forms in Europe during the Middle Ages, alongside captivity, serfdom, and other types of unfreedom. 

    [ What "common knowledge" claims, where that came from, ... ] 

    Yet into the 14th and 15th centuries, medieval Europeans continued to own slaves, trade in slaves, and enslave each other as well as non-European others. They used slaves for agricultural and artisanal labor as well as domestic, sexual, reproductive, and military service

( from an assistant professor of history whose research interests covers practices of slavery in the medieval Mediterranean, particularly the slave trade from the Black Sea to the markets of Cairo, Genoa and Venice during the thirteenth through fifteenth centuries. )

With references for you to read should you wish.