 Complete the following phrase:  In 1166, Stefan Nemanja assumed the throne, marking the beginning of a prospering Serbia, henceforth under the rule of the Nemanjić dynasty. Nemanjas son Rastko  Saint Sava, gained autocephaly for the Serbian Church in 1219 and authored the oldest known constitution, and at the same time Stefan the First-Crowned established the Serbian Kingdom in 1217. Medieval Serbia reached its peak during the reign of Stefan Dušan 1331-1355, who took advantage of the 