Gąsawa massacre The Gąsawa massacre ( , literally " the Gąsawa crime " ) was a 1227 attack on a meeting of Polish Piast dukes which was being held near the village of Gąsawa in Kujawy , Poland . The High Duke of Poland , Leszek the White , was assassinated , and Duke Henry the Bearded of Silesia was gravely wounded . Because at the time of the attack some of the victims were bathing in preparation to retire for the night , the event is also known in Polish historiography as the Gąsawa Bloodbath ( " krwawa łaźnia w Gąsawie " ) . Motive . While direct responsibility for the attack is generally ascribed by historians to Świętopełk of Pomerania , many circumstances surrounding the crime remained unexplained and controversial . Świętopełk ' s aim was to make the Duchy of Gdańsk Pomerania , which his House of Sobiesław held as regents of the Polish rulers , independent of Piast overlordship . The murder of Leszek the White , Świętopełk ' s suzerain , thus served his interests . However , several historians have pointed to Duke Władysław Odonic , who had forged an alliance with Świętopełk shortly before the attack , as the main instigator . Odonic ' s actual target would have been his uncle , Duke Władysław Spindleshanks , with whom Odonic had been involved in a long - running conflict over control of Greater Poland ( " Wielkopolska " ) . Under this hypothesis , Odonic provided information necessary for a successful attack to Świętopełk ' s men , who actually did the deed . Other historians have disputed this thesis , pointing out that Spindleshank was not harmed in the attack , that Odonic did not profit from the death of Leszek ( with whom he had had generally amicable relations ) , and that there is no record that contemporaries or the families of the slain held Odonic responsible . Rather , in this view , the blame was ascribed retroactively to Odonic several decades later , during fighting between Dukes of Silesia who were descendants of Henry , and those of Greater Poland , who were related to Odonic . A particularly puzzling fact is the absence of condemnation by ecclesiastical authorities ( some of whom were present at the meeting ) , who at that time took an active role in Polish political affairs and tended to react strongly to regicides . Outcomes . Whatever the exact circumstances of , or the responsibility for , the event , it is generally accepted that the crime contributed to the deepening of the feudal fragmentation of Poland . Świętopełk successfully cast off the control of the Piast dukes over Gdańsk Pomerania and began using the title " dux " ( rather than " regent " ) . Piast control over the area was not re - established until the Treaty of Kępno ( 1282 ) between Mściwój II of Pomerania and Przemysł II ( perhaps ironically , a grandson of Odonic ) . The death of Leszek the White undermined the authority and status of the " High Duke of Poland " ( " principat " ) , who technically ruled over all the other regional Polish dukes ; and the " seniorate " province of Kraków / Małopolska essentially became just another feudal area to be fought over . Poland , as a unified political entity , would not be re - established until the reign of Wenceslaus III or Władysław the Elbow - high at the turn of the 13th and 14th centuries .