The Ottomans entered for the first time into Wallachia in 1395. Although the invading troops were defeated somewhere in a "rovină" ("ragged marshland") in Oltenia, the chaos created by the threat of attacks allowed a group of "boyars" to put Vlad I the Usurper (1395–1397) on the throne. Thus Mircea I was forced to take refuge in Transylvania, where he agreed to be Sigismund I of Hungary's vassal. He was restored to the throne and participated in the disastrous crusade of Nicopolis organized by Sigismund I.