Wait hello,
I too have seen the pictures of this chair before, and I wondered. . ."what the ...?"
As i understand it this is the chair of Peter's martyrdom. A depiction of his inverted crucifixion. Since the Papacy insists upon being the successor of Peter, this chair, along with the better known "Chair of Peter", is symbolic of the Pope's role as successor to Peter, and also of the believer's being crucified to the world.
Regards, Everett 8)