Congress of Gniezno and its aftermath (999–1002)
Emperor Otto III held a synod in Rome where Adalbert was canonised on the emperor's request on 29 June 999. Before 2 December 999, Adalbert's brother, Radim Gaudentius, was consecrated "Saint Adalbert's archbishop". Otto III made a pilgrimage to Saint Adalbert's tomb in Gniezno, accompanied by Pope Sylvester II's legate, Robert, in early 1000. Thietmar of Merseburg mentioned that it "would be impossible to believe or describe" how Bolesław received the emperor and conducted him to Gniezno. A century later, Gallus Anonymus added that "[m]arvelous and wonderful sights Bolesław set before the emperor when he arrived: the ranks first of the knights in all their variety, and then of the princes, lined up on a spacious plain like choirs, each separate unit set apart by the distinct and varied colors of its apparel, and no garment there was of inferior quality, but of the most precious stuff that might anywhere be found."
Bolesław took advantage of the emperor's pilgrimage. After the Emperor's visit to Gniezno, Poland started to develop into a sovereign state, in contrast with Bohemia, which remained a vassal state, incorporated in the Kingdom of Germany. Thietmar of Merseburg condemned Otto III for "making a lord out of a tributary" in reference to the relationship between the Emperor and Bolesław. Gallus Anonymus emphasised that Otto III declared Bolesław "his brother and partner" in the Holy Roman Empire, also calling Bolesław "a friend and ally of the Roman people". The same chronicler mentioned that Otto III "took the imperial diadem from his own head and laid it upon the head of Bolesław in pledge of friendship" in Gniezno. Bolesław also received "one of the nails from the cross of our Lord with the lance of Saint Maurice" from the Emperor.
Gallus Anonymus claimed that Bolesław was "gloriously raised to kingship by the emperor" through these acts, but the Emperor's acts in Gniezno only symbolised that Bolesław received royal prerogatives, including the control of the Church in his realm. Radim Gaudentius was installed as the archbishop of the newly established Roman Catholic Archdiocese of Gniezno. At the same time, three suffragan bishoprics, subordinated to the see of Gniezno — the dioceses of Kołobrzeg, Kraków and Wrocław — were set up. Bolesław had promised that Poland would pay Peter's Pence to the Holy See to obtain the pope's sanction to the establishment of the new archdiocese. Unger, who had been the only prelate in Poland and was opposed to the creation of the archdiocese of Gniezno, was made bishop of Poznań, directly subordinated to the Holy See. However, Polish commoners only slowly adopted Christianity: Thietmar of Merseburg recorded that Bolesław forced his subjects with severe punishments to observe fasts and to refrain from adultery:
If anyone in this land should presume to abuse a foreign matron and thereby commit fornication, the act is immediately avenged through the following punishment. The guilty party is led on to the market bridge, and his scrotum is affixed to it with a nail. Then, after a sharp knife has been placed next to him, he is given the harsh choice between death and castration. Furthermore, anyone found to have eaten meat after Septuagesima is severely punished by having his teeth knocked out. The law of God, newly introduced in these regions, gains more strength from such acts of force than from any fast imposed by the bishops
During the time the Emperor spent in Poland, Bolesław also showed off his affluence. At the end of the banquets, he "ordered the waiters and the cupbearers to gather the gold and silver vessels [...] from all three days' coursis, that is, the cups and goblets, the bowls and plates and the drinking-horns, and he presented them to the emperor as a toke of honor [...] [h]is servants were likewise told to collect the wall-hangings and the coverlets, the carpets and tablecloths and napkins and everything that had been provided for their needs and take them to the emperor's quarters", according to Gallus Anonymus. Thietmar of Merseburg recorded that Bolesław presented Otto III with a troop of "three hundred armoured warriors". Bolesław also gave Saint Adalbert's arm to the Emperor.
After the meeting, Bolesław escorted Otto III to Magdeburg in Germany, where "they celebrated Palm Sunday with great festivity" on 25 March 1000. A continuator of the chronicle of Adémar de Chabannes recorded, decades after the events, that Bolesław also accompanied Emperor Otto from Magdeburg to Aachen, where Otto III had Charlemagne's tomb reopened and gave Charlemagne's golden throne to Bolesław.
An illustrated Gospel, made for Otto III around 1000, depicted four women symbolising Roma, Gallia, Germania and Sclavinia as doing homage to the Emperor who sat on his throne. Historian Alexis P. Vlasto writes that "Sclavinia" referred to Poland, proving that it was regarded as one of the Christian realms subjected to the Holy Roman Empire in accordance with Otto III's idea of Renovatio imperii — the renewal of the Roman Empire based on a federal concept. Within that framework, Poland, along with Hungary, was upgraded to an eastern foederatus of the Holy Roman Empire, according to historian Jerzy Strzelczyk.
Coins struck for Bolesław shortly after his meeting with the emperor bore the inscription Gnezdun Civitas, showing that he regarded Gniezno as his capital. The name of Poland was also recorded on the same coins, referring to the Princes Polonie [sic]. The title princeps was almost exclusively used in Italy around that time, suggesting that it also represented the Emperor's idea of the renewal of the Roman Empire. However, Otto's premature death on 23 January 1002 put an end to his ambitious plans. The contemporaneous Bruno of Querfurt stated that "nobody lamented" the 22-year-old emperor's "death with greater grief than Bolesław".
In 1000 Bolesław issued a law prohibiting hunting beavers and created an office called "Bobrowniczy" whose task was to enforce prince's ordinances.
