Medieval culture repeatedly drew connections between animals and moralistic qualities. The pig — an animal ubiquitously eaten by Christians throughout the Middle Ages — developed an unusually bad reputation. This detail from a 15th-century prayer book shows a woman stroking a pig. While the overall image looks benign — the larger painting is all about how farmers deliberately put their pigs into the woods to forage in the autumn — it also gets at one of the many stereotypical associations of pigs, which is that of female lust. For the record, female lust was considered A Bad Thing.
Pigs were associated with uncleanliness by Medieval people, and of course Jews and Muslims were forbidden from eating pork because of this polluting taboo. But even Christians thought that pigs were filthy, and commented that the animals liked to swallow in their own shit. This propensity took on a metaphorical idea that pigs were like people who readily gave themselves over to gluttony and lust. One miracle story from the Early Middle Ages tells of a nun who, having stolen extra food, was divinely punished with intense physical pain that only abated when she ate the plainest food available. She sees a miraculous vision of a pig eating all her stolen food, and knows that she was like the pig.
Eventually, female lust replaced mere gluttony as the top negative symbolic meaning of the pig. One French brothel advertised itself with a sign showing a pig having oral sex with a half woman-half pig. Men frequently stereotyped women as being sex-crazed in the Middle Ages. (As I already wrote, this was considered A Bad Thing.)
There were other negative associations of pigs. Sadly, they were often depicted in horrifying anti-Semitic artwork, which is ironic, considering the Jewish taboo on eating pork. The Biblical miracle stories of Jesus casting demons out of humans and into the pigs underscored ideas of pigs as irrational and devilish: stereotypes that Medieval Christians also had about Jewish people.
Sources: “Heures de Charles d’Angoulême,” by Robinet Testard, “October”, Bibliotheque Nationale de France, Getty Images. Chapter Five, _Legions of Pigs in Early Medieval Europe,_ Jamie Kreiner, Yale UP, 2020