Not all "medieval" Christmas carols are medieval in origin.
It's a common misconception that Christmas carols are very old and that the most formal ones (often in Latin) are the oldest. Not so. While the oldest hymns do appear to derive from the Latin translation of the Bible, older vernacular carols do survive. English carols are often very hard to date because the Puritans tried to suppress the celebration of Christmas in the 17th century, including traditional hymns. This may explain why some of the older English carols are so dark in tone (Coventry Carol).
Another misconception is that lyrics have survived but not music, probably because of the spotty history of music preservation prior to the introduction of formal notation. In fact, some of the melodies that survive are among the oldest types of music whereas their current lyrics are quite modern--19th and 20th century, in fact.
It's also probably no surprise that medieval carols are among the lesser carols, rather than the big hits like "We Three Kings of Orient Are" or "Hark the Herald Angels Sing" (both 19th century). Unlike the most famous carols, the older tunes also come from all over Europe, rather than almost exclusively from England or Germany.
Take, for example, "Carol of the Bells" (or "The Ukrainian Bell Carol"). This was originally a traditional Ukrainian tune entitled "Shchedryk" (Bountiful) that called in the New Year with the tale of a swallow that flies into the house and prophesies both the spring and a happy new year for those within. Ukrainian composer Mykola Dmytrovych Leontovych (1877-1921) adapted the tune for a chorus in 1916. American composer Peter Wilhousky (1902-1978) added new English lyrics about Christmas caroling in 1936 and it became part of the American carol lineup. The carol is one of a series of New Year songs that young girls would use to go caroling in Ukraine on January 13 (the New Year in the old Julian calendar).
Then, there is the sad and rather scary English "Coventry Carol". This 15th century tune is one of the oldest unadapted carols around, retaining both its original tune and original lyrics. Both were first written down in 1591, but the tradition of the Coventry plays in which it was sung goes back to at least to 1456. These passion plays (a passion play commemorates the last week of Christ's death and his subsequent resurrection) apparently included a scene about the legend of the Slaughter of the Innocents shortly after Christ's birth (Feast day: December 28). According to the New Testament, the king of that time in Judea, Herod, was a tyrant who feared usurpation. After the Wise Men visited him, prophesying the wonders of Christ's birth, he ordered all first-born boys in Nazareth slaughtered. The song was probably sung during the reenactment of this story.
See part 2 for more medieval Christmas carols and their origins and go here for reviews of collections of medieval Christmas music.
