St. Ignatius was the Bishop of Antioch. Now he was alive when the apostles were still alive as well. It is said he was a student of St. John. It was in about the year 80 AD that we hear for the first time in history the words Catholic Church. It was St. Ignatius that spoke the words Catholic Church at Antioch. He used it in a manner of speaking not instructing. Which would mean that the people there knew it was the Catholic Church.
Which brings us to this point. That the Catholic Church is the one and true church of the apostles. Which is why it is called the Apostolic Church. Which is the church the apostles started in the first century. Which means if St. Ignatius called it the Catholic Church that also means that the other apostles which were still alive also knew it as the Catholic Church at Antioch.

Ignatius, bishop of Antioch, was a prominent early Christian leader, writing letters during his journey to martyrdom in Rome around 110 AD.

Believed to have known the Apostle John, Ignatius's teachings reflect a deep understanding of apostolic tradition and early church structure.

His courageous acceptance of martyrdom, facing wild beasts in the Colosseum, became a powerful testament to Christian faith.
Ignatius emphasized the crucial role of the bishop as the center of unity and authority within the Christian community.
He stressed the importance of the Eucharist as the 'medicine of immortality' and the true body of Christ.
Ignatius vigorously opposed early heresies, particularly Docetism, affirming Christ's true humanity and suffering.
His seven surviving letters offer invaluable insights into the beliefs, practices, and organizational structure of the 2nd-century Church.
His unwavering commitment to Christ, even in the face of death, serves as an enduring model for believers.
Ignatius's writings profoundly shaped Christian theology, particularly concerning ecclesiology and the sacraments.