Carols at Christmas have been such a popular tradition for so long that it seems strange to realize that holiday carols haven't always been a part of the Christian tradition, but it's true. In fact, there was a time when Christian churches regarded the practice of singing holiday carols as a pagan custom―which in fact, it was.
The term carol describes a song of praise and joy. Certainly, holiday carols were a part of the pagan solstice celebrations, the most important of which occurred in December during the time when the days began to become longer than the nights again.
In our modern world, we can dispel darkness with a flick of a light switch and food is as available in December as in May. This wasn't the case for our prehistoric ancestors, who were less able to hunt or grow their food during the winter months, and for whom the longer dark nights posed very real threats.
Because they lived so much closer to nature than we do, they must have felt grateful indeed when winter solstice―the shortest day of the year―finally arrived and marked the beginning of increasing daylight hours. Singing holiday carols of praise and thanks, they danced around stone circles, and welcomed the return of the light.
Even though the early Christian church disapproved of carol singing, clergy members came to realize that the tradition of singing at this time of the year was so ingrained, that it made more sense to 'Christianize' the practice than forbid it. And so, holiday carols became Christmas carols.
One of the earliest Christmas carols was a song called 'Angel's Hymn', which a Catholic bishop directed to be sung at a Christmas service in the year AD 129! Early carols such as this were written and sung in Latin, which fewer people knew, and used less and less as time went by. While the practice of writing carol music continued to increase, it wasn't until medieval times that the practice of carol singing became firmly established as a Christian tradition.
St. Francis of Assisi was responsible for developing the type of holiday carol we sing today. In the early 1200s, St. Francis originated nativity plays, in which players sang songs to tell the story of the play. Because St. Francis insisted that players sing in the language of their audiences, people who attended the nativity plays were able to join in and sing along with the performers. Many of the carols we sing today retain the medieval chord patterns used then.
The new carols spread from Italy to France, Spain, Germany, and finally to England, where the practice of holiday caroling became almost an art form. Groups of English carolers began going from house to house to serenade the occupants, who frequently expressed their appreciation by inviting the carolers inside for hot beverages and holiday food. The holiday caroling tradition traveled across the Atlantic from England to America, where it remains popular to this day.