Poznań, today Poland's fifth largest city, is also one of the country's oldest cities, and was an important political and religious center in the early Polish state of the 10th century. Poznań Cathedral is the oldest church in the country, containing the tombs of the first Polish rulers, Duke Mieszko I and King Bolesław I Chrobry. Although the centre of national political power moved to Kraków in the 11th century, and later to Warsaw, Poznań remained an important regional center, being the chief city of the Greater Poland (Wielkopolska) region. It came under Prussian (later German) rule for most of the period from 1793 to 1918, during which it expanded significantly, and was also heavily fortified (as Festung Posen). The city resumed its role as a Polish voivodeship capital in the Second Polish Republic, and later, following the 1939–1945 Nazi German occupation, in the communist Polish People's Republic. Since 1999 Poznań has been the capital of Greater Poland Voivodeship. Early times and Piast Poland (to 1138) The first settlements in what is now Poznań can be traced to the late period of the Stone Age. Later various cultures developed there in the Bronze Age and Iron Age. Poznań began as a stronghold built in the 8th or 9th century AD between branches of the Warta and Cybina rivers, on what is now called Ostrów Tumski ("Cathedral Island"). Various other settlements sprang up nearby on the islands and on both banks of the Warta. In the 10th century the tribe inhabiting the region, the Polans, became dominant over other tribes in most of the area of today's Poland. Consequently, this early Polish state, ruled by Duke Mieszko I and his successors in the Piast dynasty, was centred politically on Poznań and the neighbouring Polan strongholds, particularly Gniezno and Giecz. Archaeological research shows that in the late 10th century Poznań had a ducal palace (where the Church of Our Lady now stands, opposite the cathedral), with a chapel, possibly built for Mieszko's Christian wife Dobrawa. The ceremony by which Mieszko converted to Christianity in 966, known as the Baptism of Poland, is likely to have taken place at Poznań. Following the conversion, in 968 Poland received its first missionary bishop, Jordan, who is believed to have used Poznań as his seat. Construction began of Poznań's cathedral. This was originally built in an early Romanesque style, and as Poland's first cathedral had St.