It is said that ---
(N) is said to be (n) / (adj)
Mr.A, was said to have an amazing record in that he ~, is ...
~だという驚くべき記録を持つと言われているA氏は・・・
They say that ----
It is believed to have been
It is believed to have been the world's biggest stadium.
かつては世界最大のスタジアムであったと考えられています。