In the early 13th century Poland's policy toward Prussia was activated and scored some successes. Swietopelk of Gdansk seized the estuary of the Vistula and founded on the east bank of the Nogat (one of the branches of the Vistula delta) the settlement of Zantyr. Many Polish settlers penetrated the north-eastern territories. The victor of Zawichost, the voievode (governor and commander-in-chief of a province) Krystyn of the Gozdawa clan, formed a system of defence against the incursions of the Prussians. It was a chain of small forts along the rivers Osa and Lesser Osa, with garrisons capable of holding off an enemu for some time, until the mobile force stationed in Radzyn and commanded by Krystyn himself could come to the rescue.
Polish missionaries started work along the Prussian border, originally under the direction of Archbishop Kietlicz.
In 1215 Innocent III established a special mission dicese for Prussia, headed by a monk from the Wielkopolska abbey of Lekno, a German by the name of Christian.
In 1217 Conrad of Masovia imprisoned the voievode of Krystyn and had him blinded and then executed. The motives of the crime were not clear. Perhaps the voievode, an outstanding leader, had gained too much influence and the prince felt threatened by him. Conrad's behavior was always characterized by extreme cruelty.
The death of the voievode Krystyn put an end to the border defence system which he had organized. Prussian raids became more frequent and intolerable. No one knew how to deal with them, as Boleslaw the Wrymouth had dealt with Pomerania a hundred years earlier. After the death of Leszek the White, Conrad turned his attention southward, toward Cracow and Sandomierz, entrusting the solution of the Prussian problem to others.
In 1239, twenty-two years after the murder of the voievode, one of Conrad's chief accusers, the reverend Czapla, the prince's chancellor, suffered a similar fate. Conrad accused him of plotting and, without any trial or written verdict, ordered him tortured and hanged. The church excommunicated Conrad for his savage deed and placed an interdict on the diocese of Plock. The prince bowed to pressure and granted new privileges to the archbishop.