In 1370, following the last will of Casimir the Great, King Louis I of Hungary handed the Land of Wieluń to Duke of Opole, Władysław Opolczyk. In the same period, the Archbishop of Gniezno, Jarosław of Bogoria and Skotnik built a manor house in Wieluń. The town remained in the hands of Władysław Opolczyk until 1395, when it was returned to Poland. Wieluń quickly developed, in the 1390s a Paulists church together with an abbey were built, and in 1413, Archbishop Mikołaj Trąba moved the ancient collegiate church from Ruda to Wieluń. In the 1440s and 1450s, Wieluń was frequently destroyed in raids of Silesian dukes. By that time, it had already been an important center of commerce and government.