 Complete the following phrase:  After the Mongol invasion of Rus, the principality became largely ruined, however it remained intact throughout repeated Tatar invasions. Unfortunately, not much is known about this period as Severia was rarely mentioned in written accounts of the 13th century. By the mid 14th century, it was already part of the Grand Duchy of Lithuania as appanage duchy, whose Gediminid princes Ruthenian-speaking and Orthodox by religion established their capitals in the cities of Novhorod-Siverskyi, Starodub, and Trubchevsk. During the 1501-1503 Lithuanian-Muscovite wars, an ally of the Grand Duchy of Lithuania, Khan of Great Horde Sheikh Ahmed destroyed the duchys capital Novgorod-Siverskyi which by that time was controlled by Muscovites. After the Lithuanian defeat at the 