 Prince Petru also expanded his rule southwards to the Danube Delta.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.