Peter as its patron. The first rulers of Piast Poland – Mieszko I, Bolesław I and Mieszko II – are buried beneath the cathedral. Gniezno was created an archbishopric at the Congress of Gniezno in 1000, by agreement between Bolesław I and Holy Roman Emperor Otto III. However Jordan's successor Unger remained as Bishop of Poznań independent of Gniezno, although it is not clear whether this continued to be a missionary bishopric subordinate to the Pope, or was attached to the Bishopric of Magdeburg. With Mieszko II's death in 1034, which probably occurred in Poznań (and may have been the result of an aristocratic plot), the country entered a period of anarchy and pagan reaction, which caused much devastation in the region. In 1038 Bretislaus I, Duke of Bohemia invaded, sacking and destroying Poznań and Gniezno. When Poland's unity was restored by Casimir the Restorer in 1039, the capital was moved to Kraków, which had been relatively undamaged by the troubles. Poznań and Gniezno were rebuilt, and in spite of the decline in the region's political importance, Poznań remained an important economic center. In the period of fragmentation of Poland (1138–1320) Under the testament of Bolesław III, in 1138 Poland was divided into separate duchies under the late king's sons. Poznań and its surrounding region (though without Gniezno and Kalisz) became the domain of Mieszko III the Old, the first of the Dukes of Greater Poland. The period saw much turbulence and fighting among the dukes, with the duchies and their subdivisions (such as the duchies of Poznań, Gniezno and Kalisz) frequently changing hands. Mieszko was High Duke of all Poland at various times between 1173 and his death in 1202, by which time he had also gained control of Gniezno and Kalisz, thus making Poznań a centre of power in a region covering the whole of Greater Poland. However the instability would continue throughout the 13th century. Poznań at this time was still essentially the stronghold on the cathedral island. However, by the end of the 12th century various trade and craft settlements had developed around it, including those of St. Gotard, St. Martin and St. Adalbert (Wojciech) on the left bank of the Warta river, and Śródka on the right bank. The name Śródka derived from the Wednesday markets which were held there (środa is Polish for "Wednesday"). Beyond Śródka was the Church of St. John (formerly of