Perhaps even more so than in Classical times, it’s not so much a matter of monsters per se in the Middle Ages, but monstrosities rather. We do have the blood-drinking, Geat-eating Grendel and his swampy mother in Beowulf, emerging from folktale and given the properly improper genealogy of belonging to the race of Cain by the vaguely Christianizing narrative filter. For a perspective on dragons and reptiles, see the Dinosaur-Dragon Abstract (or the article published in Popular Culture Review). Arthurian knights encounter some bizarre spectacles, but no “classic” monsters take hold of our consciousness in these romances, nor in those of the better-travelled infidel-slayers and Mandevillian map-trotters.
We do find monstrosity, however, in the form of personifications and grotesques. In addition to architectural monsters in the form of gargoyles (always outside the cathedrals and therefore associated with the dangerous world outside the sanctuary of the Church) and similar perversions of God’s creatures decorating the margins of illuminated manuscripts, the bestiaries contain bizarre creatures alongside actual ones. Here the lines between natural science and theology blur, so that the qualities attributed to creatures real and legendary are read simultaneously as lurid quirks and as glimmers of a more pervasive Christian text.
Obversely, abstractions of a religious nature take grotesque form in literature and in artistic depiction –particularly the Seven Deadly Sins, which are given intentionally repulsive forms in lyrics and in Langland’s Piers Plowman. Thus we inherit archetypal images of goat-like Lechery, biliousGluttony, the droop-eyed slacker Sloth, and so forth. These make cameo appearance on parade, but are meant more for contemplation than to function as true “monsters” in the ways we will come to expect.
Delahoyde, Michael. “Medieval Dragons and Dinosaur Films.” Popular Culture Review 9.1 (February 1998): 17-30.