On 14 April 966, Mieszko I – the first historical ruler of Poland, was baptized. This was followed by the baptism of the Polish people and the Christianization of that land. Where this baptism took place is a matter of historical debate, with Gniezno, Poznań, Ostrów Lednicki, Cologne, Regensburg and Rome being suggested.

Mieszko saw in Catholicism a way of uniting the Polish people in a common faith and of supporting his authority over Poland. Moreover, adopting Christianity gave it some protection against the strong German Holy Roman Empire on its borders which could have used Christianization as a motivation for attacking the Poles and putting them under its control. Other motivations suggested for the decision to be baptized are a desire to improve relations with the Czech kingdom of Bohemia to which his wife Dobrova belonged or a desire to weaken the powerful pagan priests.

Of course, since Poland chose to adopt Catholicism as a result of Czech missionaries from the West as opposed to its neighbor Russia which took the faith from the East, this will have profound effects on the future relations between these two peoples and the understanding of Slavic nationalism – these Czech missionaries had accompanied Dobrava when she married Mieszko in 965. Thus, Poland will adopt Latin liturgical traditions and the Latin alphabet whereas Russia will adopt the Slavonic alphabet and the liturgical traditions of Constantinople.

The baptism of Mieszko also may have had an influence on the Polish celebration of Dyngus Day. By tradition Mieszko was baptized on Easter Monday and the dousing of young women with water on Dyngus Day, celebrated on Easter Monday, may be related to this event.

For more on Mieszko and his baptism.