castel sant'angelo or mausoleum of hadrian, parco adriano, rome, italy

castel sant#39aph39#angelo mausoleum hadrian parco adriano rome italy emperor roman medieval fortress ancient architecture hadrian#39aph39#s tomb papal defensive tower tiber river history cylindrical structure renaissance modifications military stronghold apartments vatican city empire historical monument engineering cultural heritage fortification iconic landmark legacy refuge castle protection antiquity historic emperors architectural transformation walls monuments art bridge ponte public museum treasure ruins defense system relics evolution funeral significance castle river tiber