Gothic Architecture began in France around the 12th Century, originally known as "The French Style". This beautiful website explores this wonderful period or style, including architecture terms and links to stunning examples:
Churches were often built as elaborately, or even more elaborately, than castles. Cathedrals were churches that contained a seat for (or held the office of) a bishop, a position of great power, often acting as a councelor (or chancellor) to the monarch. Although cathedrals held positions of importance, not all were massive works of art. Since churches collected taxes and tithes from local citizens, they often became very wealthy and powerful. They also found power through the use of relics (supposedly) belonging to saints which led to pilgrimmages.
A listing of medieval churches: