One Monday at the very end of the fourteenth century, John Green, the perpetual vicar of the prebendal church of Wistow, and John Keleby, the chaplain and parish clerk of the same church, were saying the verses of the day. Then Green stumbled over his words, Keleby laughed, and Green threw his psalter at the clerk. This unseemly incident may well have gone unrecorded, except for the fact that the book ‘slightly broke the skin of his [Keleby’s] head, so that a little blood appeared on the surface, but slight in quantity’. Consequently, the two men went together to Cawood to tell the archbishop of York what had happened. Archbishop Richard Scrope determined that the church had been polluted by the violence committed therein; it must therefore be reconciled.

The idea that a church could be contaminated by bodily fluids was an old one, with its roots in Levitical prohibitions; the idea that a polluted church should be ritually reconciled probably derived from the same source, specifically the ritual for purifying a leper's house. During the course of the Middle Ages, such ideas became firmly entrenched in canon law: the early eleventh century Excerptiones Ecberti Eborcensi archiepiscopi (which were probably written by Wulfstan of York) specify that reconsecration was necessary if a church was polluted by murder or adultery, and the idea that emissions of blood and semen (along with fire and the burial of an infidel or excommunicate) could contaminate a church or churchyard was restated by all the major canonists, including Gratian.

By the later Middle Ages, the main concerns seem to have been bloodshed and sex, both of which could be deeply problematic, and not just because of cultural taboos about bodily fluids. Once a church had been consecrated (that is, as William Durandus put it, once it had been ‘dedicated in a ceremony by the hands of a bishop, and sanctified by God’), it became a sacred space, suitable for activities such as praising God and administering the sacraments. Moreover, as Daniel Thiery has argued, only God was entitled to enact violence in such a place; consequently, prohibitions on violence formed an important part of the consecration ceremony, and acts that would be licit in the secular world were sinful here.