The celebration of name days has been a tradition in Catholic and Eastern Orthodox countries since the Middle Ages, and has also continued in some measure in countries, such as the Scandinavian countries, whose Protestant established church retains certain Catholic traditions. The name days originate in the list of holidays celebrated in commemoration of saints and martyrs of the church. For example, the name Karl or Carl is celebrated in Sweden on 28 January, the anniversary of the death of Charlemagne (Charles Magnus, i.e., "the great"). The church promoted the celebration of name days (or rather saints' feast days) over birthdays, as the latter was seen as a pagan tradition.
Where name days occur, official lists contain the current assignations of names to days. There are different lists for Finnish, Swedish, Sámi, and other countries that celebrate name days, though some names are celebrated on the same day in many countries. From the 18th century and onwards the list of name days has been modified in Sweden and Finland.
Name day - Wikipedia
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Do you know your name day?