The Coventry Carol is a song from the Coventry mystery play cycle. There are references to the cycle from 1392 onwards, but the earliest surviving text dates from 1534. The song is from the Pageant of the Shearmen and Tailors and refers to the Massacre of the Innocents.
The song later became associated with Christmas, and in 1940 a performance was broadcast from the bombed out ruins of Coventry Cathedral.
(Pieter Bruegel the Elder - Massacre of the Innocents, Public Domain)