it all depends what you mean by largest, but the largest religious structure is St PetersBbasilica in Rome and is considered to big to be a Cathedral. So, the answer may be St John the Divine in New...
A cathedral (French cathédrale from Lat. cathedra, "seat" from the Greek kathedra (καθέδρα), seat, bench, from kata "down" + hedra seat, base, chair) is a Christian church that contains the...
The foundation stone was laid on 28 April 1220, and by 1258 the nave, transepts and choir were complete. The west front was ready by 1265. The cloisters and chapter house were completed around 1280....