Victor R. Claveau, MJ
The Roman Catholic Church has infallibly defined the interpretation of Matthew 16:18.
The Council of Ephesus, 432 AD
No one doubts, in fact, it is obvious to all ages that the holy and most Blessed Peter, head and Prince of the Apostles, the pillar of faith, and the foundation of the Catholic Church, received the keys of the kingdom from our Lord Jesus Christ, the savior and redeemer of the human race.
First Vatican Council, 1870
Therefore if anyone says that the blessed Apostle Peter was not constituted by Christ the Lord as the Prince of all the Apostles and the visible head of the whole Church militant, or that he received immediately and directly from Jesus Christ our Lord only a primary of honor and not a true and proper primacy of jurisdiction: anathema sit. (The First Dogmatic Constitution of the Church of Christ, Ch. 2)