Periods of renewal in the Church are also intense moments of catechesis. In the great era of the Fathers of the Church, saintly bishops devoted an important part of their ministry to catechesis. St. Cyril of Jerusalem and St. John Chrysostom, St. Ambrose and St. Augustine, and many other Fathers wrote catechetical works that remain models for us.
Source: Catechism of the Catholic Church (Vatican.va)