Constantine VII's De Administrando Imperio, written around 950 AD, tries to define precisely the whole land of the Hungarians, or "Tourkia". Constantine described the previous inhabitants of Hungary ("e.g.", the Moravians), described early Hungarian settlements and neighbors, and located Hungarian rivers (Temes, Maros, Körös, Tisza, Tutisz). Constantine had much more knowledge about the eastern parts of Hungary; therefore, according to one theory, "Tourkia" did not mean the land of the whole federation, but a tribal settlement and the source of the description of Hungary could have been Gyula whose tribe populated the five rivers around 950. According to another hypothesis, mainly based on Constantine's description, the Hungarians started to really settle western Hungary (Transdanubia) only after 950, because the eastern part of the country was more suitable for a nomadic lifestyle.