 His brother Roman I conquered the Hungarian-ruled Cetatea Albă in 1392, giving Moldavia an outlet to the Black Sea, before being toppled from the throne for supporting Fyodor Koriatovych in his conflict with Vytautas the Great of Lithuania.Under Stephen I, growing Polish influence was challenged by Sigismund of Hungary, whose expedition was defeated at Ghindăoani in 1385; however, Stephen disappeared in mysterious circumstances.Although Alexander I was brought to the throne in 1400 by the Hungarians (with assistance from Mircea I of Wallachia), this ruler shifted his allegiances towards Poland (notably engaging Moldavian forces on the Polish side in the Battle of Grunwald and the Siege of Marienburg), and placed his own choice of rulers in Wallachia.