Saint Casimir's Day, on the anniversary of the death of Saint Casimir, the patron saint of Lithuania. It is celebrated on March 4. On this day famous Kaziuko mugė is held Saint Casimir Saint Casimir Jagiellon, Patron Saint of Poland and Lithuania, was prince of Poland and Grand Duchy of Lithuania. ... Kaziuko mugÄ— (English: , Polish: ) - is a biggest annual Lithuanian folk crafts fair dating back to the beginning of the 17th century, then held at the two main market places of Vilnius, Lithuania, as well as in the city streets. ...