The Catholic Church has defined the Gates of Hell mentioned in Matthew 16 are heretics.
Pope Vigilius, Second Council of Constantinople, 553:
“… we bear in mind what was promised about the holy Church and Him who
said the gates of Hell will not prevail against it (by these we
understand the death-dealing tongues of heretics)…” Decrees of the Ecumenical Councils, Vol. 1, p. 113.
Pope St. Leo IX, Sept. 2, 1053:
“The holy Church built upon a rock, that is Christ, and upon Peter…
because by the gates of Hell, that is, by the disputations of heretics
which lead the vain to destruction, it would never be overcome.” Denzinger, The Sources of Catholic Dogma, B. Herder Book. Co.,
Thirtieth Edition, 1957, no. 351.
St. Thomas Aquinas (+1262):
“Wisdom may fill the hearts of the faithful, and put to silence the
dread folly of heretics, fittingly referred to as the gates of Hell.”
(Intro. To Catena Aurea.) The Sunday Sermons of the Great Fathers,
Regnery, Co: Chicago, IL, 1963,Vol. 1, pp. xxiv