He could even less afford to do so after 962, when Otto was crowned Roman Emperor by the Pope. This was a largely symbolic act, but one charged with significance, and Mieszko, who was aware of the political and cultural benefits Christianity had brought his Czech neighbours of Bohemia, appreciated this. Only by adopting Christianity himself would he be able to avoid war with the Emperor, and at the same time provide himself with a useful political instrument. In 965 he sought the approval of Otto and married the Bohemian Princess Dobrava. The following year, 966, Mieszko and his court were baptised. The Duchy of Polonia became part of Christendom.
Mieszko nevertheless continued to pursue his own aims, even where they conflicted with those of the Empire. One of these was to gain control of as much of the Baltic coast as possible. He invaded Pomerania, but this led to confrontation with the Margrave of the German northern march, who was attempting to conquer the area for the Empire. Mieszko defeated him at Cedynia in 972 and reached the mouth of the Oder in 976. The Margrave called on his new master Otto II for assistance, and the latter mounted an expedition against the Poles. Mieszko defeated him too in 979, and became master of the whole of Pomerania. He con—tinued to advance along the coast until he joined up with the Danes, who had been extending their dominion eastward. He ensured good relations with his new neighbours by giving his daughter Świętosława in marriage to King Eric of Sweden and Denmark (after Eric’s death, she would marry Swein Forkbeard, King of Denmark, and bear him a son, Canute, who visited Poland in 1014 to collect a force of three hundred horsemen who would help him reconquer England).
The first ruler of Christian Poland was a remarkable man. Consistently successful in war, Mieszko did not neglect diplomacy, involving powers as distant as the Moorish Caliphate of Cordoba in Spain in his schemes. His last enterprise was to invade and absorb the lands of the Slenzanie. There in 992 he drew up a document,
The Pope was to prove immensely useful to Mieszko’s son and successor, Bolesław the Brave, who carried on his work with flair. In 996 a monk called Adalbertus (originally Vojteh, a Bohemian prince) appeared at Bolesław’s court. As he had been sent by Pope Sylvester I on a mission to evangelise the Prussians, a non-Slavic people inhabiting the Baltic seaboard to the east of the mouth of the Vistula, Bolesław received him with due honours before sending him on his way. The Prussians made short work of putting the missionary to death. On hearing the news, Bolesław sent to Prussia and bought the remains of the monk for, allegedly, their weight in gold. He then laid them to rest in the cathedral at Gniezno.
When Pope Sylvester heard of this, in 999, he canonised Adalbertus. He also took the momentous step of elevating Gniezno to the level of an archbishopric, and creating new bishoprics at Wrocław, Kołobrzeg and Kraków. This effectively created a Polish province of the Church, independent of its original tutelary German diocese of Magdeburg. It also strengthened the Polish state, as ecclesiastical networks were prime instruments of communication and control. In Poland, the first parishes were established beside castles which were centres of royal administration, a connection between religious and temporal power which is enshrined in the etymology of the Polish word for ‘church’—
The new Emperor Otto III had been a friend of Adalbertus, as well as of Pope Sylvester, and in the year 1000 he came on a pilgrimage to the saint’s shrine at Gniezno. His visit is described by the chronicler Gallus, who wrote: