On March 7, 1000, the Congress of Gniezno began. The Polish Duke Bolesław I and Emperor Otto III met during the emperor’s pilgrimage to the tomb of St. Adalbert. The congress lasted until March 15, 1000.
St. Adalbert became the first Slavic bishop to become a saint. His body, bought back by Bolesław from the Prussians for its weight in gold, was put into a tomb at Gniezno Cathedral, which became the ecclesiastical center of Poland.
Pilgrimage of Emperor Otto III to the grave of Bishop Adalbert and a meeting with Duke Bolesław the Brave and his sons in order to obtain the relics of the martyr. Otto III also wanted to win over Bolesław for the implementation of his plans for a universalist Western Empire, which was to consist of the provinces of Gaul, Romagna, Germania, and Sclavinia. During the congress, Otto III put the imperial diadem on Bolesław’s head and gave him a copy of the Lance of St. Maurice – one of the symbols of imperial power.