The monastery complex in Strzelno with the Basilica of the Holy Trinity and the Rotunda Church of St. Procopius is dated by both historians and archaeologists to the turn of the 12th and 13th centuries. Only a few elements of the original equipment have survived. All of them show a number of formal and conceptual analogies with the Romanesque decorations of the Benedictine monastery in Andlau in Alsace. Its interior, dating back to the second half of the 12th century, is attributed to the school of William of Modena, one of the leading artists of the Romanesque era. The evolving style of the Alsatian school gives it a distinct identity, which seems to be reflected in Strzelno. Both the wide range of motifs of complex Lombard, Italian, classical, Byzantine and Burgundian origins and the use of sophisticated construction techniques strongly confirm our thesis that the builders of the Strzelno Abbey must have been the successors of the northern Italian tradition.