What Exactly was the Rock?

Peter:(Matthew 16:16)“You are the Messiah, the Son of the living God.” Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in Heaven. And I tell you that you are Peter, and on this rock I will build my church,..."

Mary:(John 11:27)“Yes, Lord,” she replied, “I believe that you are the Messiah, the Son of God, who is to come into the world.”

The rock is the confession, not Peter!