When did Lithuania officially adopt Christianity?

Lithuania officially adopted Roman Catholicism in 1387, when the Grand Duke Jogaila formally introduced the faith to his subjects following his agreement to unite with Poland.12

While the chieftain Mindaugas had accepted Christianity in 1251 and was crowned in 1253, this was a temporary conversion; he was assassinated a decade later, and the nation reverted to its traditional pagan practices. Consequently, the 1387 event is recognized as the official adoption of Christianity that integrated Lithuania into the Latin Christian world.321