I'm cutting this from an essay that is currently too long, an essay that begins with a somewhat extraneous riff on why "race" should be a term used to describe the differentiations of peoples in the Middle Ages. Whenever I say this, someone always asks "What about slavery? Doesn't chattel slavery impact the modern use of race in a way that cannot be true for medieval peoples?"
Here are some thoughts. You might also want to read Eileen's post on the Redress Project alongside them, and/or click on "race" in the Quick Subject Links at your right.
It could be argued that a period that did not inherit the legacy of institutionalized slavery based upon skin color could not possibly have conceptualized race in the modern sense of the word.
True, the British Isles of the twelfth century witnessed nothing like the plantation system that would force the movement of millions from sub-Saharan Africa. The first Norman-appointed Archbishop of Canterbury, Lanfranc, convinced a reluctant William the Conqueror to prohibit the lucrative slave trade. Yet like most of Europe Britain lived with a memory of institutionalized slavery, the byproduct as well as the catalyst of endemic internal and external warfare.(1) Forced servitude was conducted on a relatively small scale and practiced without regard to national origin. Before their unification into a single kingdom, the Anglo-Saxons enslaved each other as well as their neighbors. The Old English word wealh, destined eventually to become the noun Welsh, could also designate a Briton slave, such as those captured when Æthelstan conquered the southwest in the tenth century.(2)
Slavery was an integral part of the medieval west's plunder economies. Saint Patrick arrived in Ireland not as a missionary but as captive, abducted from his father's estate in Britain when he was sixteen years old. Pope Gregory would never have had his famous encounter with beautiful English boys for sale in the Roman marketplace had not marauding for slaves been an expansive international business. Moriuht, the story of an Irish husband and wife captured by Vikings and sold as slaves, eventually freeing themselves to settle in Normandy, survives in an account by their hostile neighbor, the poet Garnier of Rouen. The church successfully suppressed much slaving activity by the twelfth century, but could not wholly eliminate it. William of Malmesbury writes that Godwine, destined to father the future King Harold, had in his youth been married to a sister of Cnut who accumulated great wealth by purchasing slaves in England and then shipping them for resale to her native Denmark.(3) Welsh warlords forced their human booty -- sometimes Welsh, sometimes English or Norman -- into servitude.(4) The practice was happily continued by their English enemies, although slavery in England vanished long before its disappearance in Wales, Ireland, and Scotland(5). This kind of servitude was not necessarily predicated upon the idea that whole groups are born to subservience because of differences carried in the body and manifested through an inferior culture. Yet slavery in its relation to medieval race is complicated (6). Even when groups did not make judgments about identity based solely upon general differences in skin color or physiognomy, they nonetheless seldom avoided the creation of mythologies that entwined cultural and bodily differences.
(1)David Pelteret puts it well: "Slavery can be said to have been a normal feature of early mediaeval European societies" (Slavery in Early Mediaeval England 15). On William, Lanfranc, and the slave trade, see 78. As Pelteret makes clear, just because slavery was decreed illicit did not mean that it stopped in practice for quite some time. Irish slave markets operated until perhaps 1170, stocked mainly with English captives.
(2)Pelteret, Slavery in Early Mediaeval England 70 and appendix I, "wealh."
(3)William disliked Earl Godwine, and this attack on his Danish first wife may simply be an attempt to render a foreigner as detestable as possible, but William will later accuse the English nobles in general of a similar practice, selling the "common people ... off to distant parts." Deeds of the Kings of the English, 2.200, 3.245.
(4) R. R. Davies, The First English Empire, 122-23. Again, though, the accusation of slaving raids is often made by an enemy in order to represent a group as uncivilized and therefore in dire need of subjugation. Cf. the narration of Welsh rebellion at the death of king Henry in the Gesta Stephani, a pro-English account of Stephen's reign: "[The Welsh roved] as plunderers through the whole district ... old men they exposed to slaughter or mockery; the young of both sexes they delivered over to chains and captivity" (1.9).
(5) John Gillingham, The English in the Twelfth Century 13-14, 45-47
(6) On Iceland see Jenny Jochens, "Race and Ethnicity in the Old Norse World" and on Italy Steven A. Epstein, Speaking of Slavery: Color, Ethnicity, and Human Bondage in Italy.