 After Jogaila's baptism, he was known in Poland by his baptismal name Władysław and the Polish version of his Lithuanian name, Jagiełło.The union strengthened both nations in their shared opposition to the Teutonic Knights and the growing threat of the Grand Duchy of Moscow.Vast expanses of Rus' lands, including the Dnieper River basin and territories extending south to the Black Sea, were at that time under Lithuanian control.