Great Moravia (, – megale Moravia, , ) or Great Moravian Empire,; both are historiographical terms, formal name is unknown, simply Moravia, was the first, predominantly Slavonic, major state to emerge in the area of Central Europe". Its core territories were located on the northern Morava River along the present-day border of the Czech Republic and Slovakia. However, its extent and location have been called into question. The rival theories place its centre at the south of the river Danube or the Great Hungarian Plain. The exact date of the founding of the Moravian state is controversial, but it is supposed that the state building process was completed in the early 830s under Mojmir I (r. 820s/830s–846), who is the first known Moravian ruler.