Władysław II Jagiełło
Baptism and marriage

Jogaila's Russian mother Uliana of Tver urged him to marry Sofia, daughter of Prince Dmitri of Moscow, who required him first to convert to Orthodoxy. That option, however, was unlikely to halt the crusades against Lithuania by the Teutonic Knights, who regarded Orthodox Christians as schismatics and little better than heathens. Jogaila chose therefore to accept a Polish proposal to become a Catholic and marry the eleven-year-old Queen Jadwiga of Poland. The nobles of Lesser Poland made this offer to Jogaila for many reasons. They wanted to neutralize the dangers posed by Lithuania itself and to secure the fertile territories of Galicia–Volhynia. The Polish nobles saw the offer as an opportunity for increasing their privileges and avoiding Austrian influence, brought by Jadwiga's previous fiancé William, Duke of Austria.

On 14 August 1385 in Kreva Castle, Jogaila confirmed his prenuptial promises in the Union of Krewo (Union of Kreva). The promises included the adoption of Christianity, repatriation of lands "stolen" from Poland by its neighbours, and terras suas Lithuaniae et Russiae Coronae Regni Poloniae perpetuo applicare, a clause interpreted by historians to mean anything from a personal union between Lithuania and Poland to a complete incorporation of Lithuania into Poland. The agreement at Kreva has been described both as far-sighted and as a desperate gamble.

Jogaila was duly baptised at the Wawel Cathedral in Kraków on 15 February 1386 and from then on formally used the name Władysław or Latin versions of it. The marriage took place three days later, and on 4 March 1386 Jogaila was crowned King Władysław by archbishop Bodzanta. He was also to be legally adopted by Jadwiga's mother, Elizabeth of Bosnia, so retaining the throne in the event of Jadwiga's death. He was the first Lithuanian to be crowned as the King of Poland. The royal baptism triggered the conversion of most of Jogaila's court and noblemen, as well as mass baptisms in Lithuanian rivers, a beginning of the final Christianization of Lithuania. Though the ethnic Lithuanian nobility were the main converts to Catholicism—both paganism and the Orthodox rite remained strong among the peasants—the king's conversion and its political implications created lasting repercussions for the history of both Lithuania and Poland. On 22 February 1387, he banned Catholics from marriages with Orthodox, and demanded those Orthodox who previously married with the Catholics to convert to Catholicism.
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