Was the Pope voted to be Infallible by clergy or did the Pope himself Proclaim Infallibility?

in the late 1800s. the council reaffirmed the infallibility of the pope , this has always been known as far back as the 1st. century, but with the onslaught of breakaway religions from the reformation and the anti catholicism it had to be made public for the benefit of all. revert back to matthew 16;19