It's so unpopular today that receiving it as a gift has become a joke, but fruitcake has been beloved since the days of ancient Rome, where barley marsh was mixed with pine nuts and raisins.
Its popularity spread throughout Europe, but it wasn't until 1490 that Catholics were allowed to put butter on it--when Pope Innocent VIII wrote a letter permitting the Saxons to use milk and butter when making their fruitcakes.
When Great Britain started importing sugar from the American colonies in the 16th century, fruitcakes became immensely popular...and for some, the bane of Christmas cuisine.