original: construction was completed in 1254 under frederick 's son , conrad iv of germany .
simplifications: construction was finished in 1254 under frederick 's son , conrad iv of germany . construction was finished in 1254 under frederick 's son , conrad iv of germany . construction was completed in 1254 under frederick 's son , conrad iv of germany . construction was completed in 1254 during the reign of conrad iv of germany . building was finished in 1254 under frederick 's son , conrad iv of germany . frederick 's son , conrad iv , of germany completed the construction in 1254 . construction was completed in 1254 under frederick 's son , conrad iv of germany . under frederick 's son conrad iv of germany , the constrution was completed in 1254 .