Treaty of Dubysa The Treaty of Dubysa or Treaty of Dubissa ( ) consisted of three legal acts formulated on 31 October 1382 between Jogaila , Grand Duke of Lithuania , with his brother Skirgaila and Konrad von Wallenrode , Marshal of the Teutonic Knights . During the Lithuanian Civil War ( 1381 – 1384 ) , Teutonic Knights helped Jogaila and Skirgaila to defeat his uncle Kęstutis with his son Vytautas . Trying to realize promises given by Jogaila during the war , Teutonic Knights organized the negotiations for the treaty . The acts were signed after six days of negotiations on an island in the mouth of the Dubysa River . The treaty was never ratified and never came into effect . The war resumed in summer 1383 . Terms . In the first act Jogaila promised to baptize himself and convert the Grand Duchy of Lithuania to Christianity within four years . Samogitia , land that physically separated the Teutonic Knights in Prussia from uniting with its branch in Livonia , was ceded to the Knights up to the Dubysa River by the second act . It was the first time that during the 100 - year crusade Lithuania gave up Samogitia . The third act formed a sort of four - year military alliance – both sides promised to help each other against their enemies . Jogaila also agreed not to start a war without Order ' s approval . Such provisions were limiting Jogaila ' s sovereignty . Some historians even suggested that such agreement would establish lord – vassal relationship . All three acts ( only two originals survive , the third is known from a transcript made in 1410 ) were signed by all sons of Algirdas and Uliana of Tver ( Jogaila , Skirgaila , Kaributas , Lengvenis , Kirigaila , Vygantas , and Švitrigaila ) and by Hanul , merchant from Vilnius who opened the city gates in June 1382 allowing Jogaila to depose Kęstutis . Uliana signed only the act granting Samogitia to the Order . Lithuanian historians Danilevičius and Jonynas raised doubts whether this act is authentic or forgery from 1410s , but their thesis is not widely accepted . Ratification and aftermath . Kęstutis died in Kreva prison on 15 August 1382 while Vytautas managed to escape few months later and asked the Knights for help and protection . This gave another advantage for the Knights , who pushed for ratification ( placing of official stamps ) of the treaty . Five times the Grand Master proposed a date , but Jogaila continuously refused . The final meeting was scheduled to take place on 19 July 1383 on the same island as original negotiations . Jogaila arrived as agreed , but the Teutonic delegation , led by Grand Master Conrad Zöllner von Rothenstein , got stuck near Christmemel ( Skirsnemunė ) , just a few miles away from their destination , due to shallow water in the Neman River . Insulted Jogaila refused to move from his location and meet the Grand Master . The parties separated . Teutonic Knights declared war on 30 July . They baptized Vytautas and supported his struggle against Jogaila to reacquire his patrimony . Eventually Vytautas and Jogaila reconciled in summer 1384 : Vytautas re - acquired his father ' s lands except for Trakai and Jogaila was crowned as King of Poland in 1386 . It is not entirely clear why diplomatic talks between Jogaila and the Knights broke down . Some suggested that Jogaila already knew about the opportunity to marry Jadwiga of Poland and become Polish King . Others argued that Uliana , mother of Jogaila , disapproved of baptism in Catholic rite as she was an Orthodox . Yet others pointed to Masovia where tensions rose as Jogaila started a war against Siemowit IV , who supported Vytautas and was friendly with the Knights , and Order ' s attempt to play Vytautas against Jogaila .