The present work aims to study one of the basic problem of the medieval Polish ecclesiastical hierarchy, the formation of the first (arch)bishopric centers, the construction process of the ecclesiastical hierarchy. Two different level are to be distingished in this process, the first, the foundation of Poznań supported by Otto I’s imperial-eccliastical policy which attached the Polish territories to Magdeburg and the imperial hierarchy. On a second level, around the first millenium, the foundation of the archbishopric seat at Gniezno, by Otto III referrs to a new imperial and ecclesiasical idea, the development of the Orbis Christianus by the organization of independent ecclesiastical province of Poland. The present study examinates also if this double level has influenced the further development of the hierarchy and contributed to the dichotomy which is clearly detected in the 12th century.