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Events on Sunday 18 January 1401 1
1401Union of Vilnius and RadomLithuania and Poland renew their dynastic union under Vytautas and JogailaLithuanian nobles meeting at Vilnius on 18 January 1401 confirmed Vytautas as Grand Duke under the ultimate authority of King Jogaila of Poland, with Lithuania reverting to Poland if Vytautas died without an heir. Polish nobles ratified the agreement at Radom in March. The union strengthened cooperation between the two states ahead of renewed conflict with the Teutonic Knights.