He was given the mandate of restoring the diocese to obedience to the Pope after succeeding a popular liberal bishop who had supported Italian unification and the surrender of the Pope's temporal powers.

[1] Rota succeeded Bishop Giovanni Corti in Mantua, a liberal who had strongly supported the unification of Italy and hoped that the Pope would voluntarily give up his temporal powers.

Corti had died three years earlier, and it had been difficult to find a successor.

[2] Pietro Rota was not granted the exequatur from the civil authorities, and therefore was not allowed to reside in the bishop's palace.

[3] Rota founded the periodical Il Vessillo Cattolico (The Catholic Banner), which was published from 1872 to 1876.