Grand Prince Stefan Nemanja (1166-1196) succeeded in uniting Serbian lands, gaining independence from the declining Byzantine Empire. He was succeeded by his middle son Stefan, while his first-born son Vukan was given the rule of the Zeta region (present-day Montenegro). Stefan Nemanja's youngest son Rastko became a monk (as Sava), turning all his efforts to spread religion among his people. Since the Catholic Church already had ambitions to spread its influence to the Balkans as well, Stefan took advantage and obtained the royal crown from the Pope in 1217. In Byzantium, Sava managed to secure autocephaly (independence) for the Serbian Church and became the first Serbian archbishop in 1219. In the same year Sava issued the first constitution in Serbia, the "Zakonopravilo". Thus the medieval Serbian state acquired both forms of independence: political and religious.