By 1006, Stephen consolidated his power, and started sweeping reforms to convert Hungary into a Western feudal state. The country switched to using the Latin language, and until as late as 1844, Latin remained the official language of Hungary. Around this time, Hungary began to become a powerful kingdom. Ladislaus I extended Hungary's frontier in Transylvania and invaded Croatia in 1091. The Croatian campaign culminated in the Battle of Gvozd Mountain in 1097 and a personal union of Croatia and Hungary in 1102, ruled by Coloman i.e. Könyves Kálmán.