Catechism of the Catholic Church §1230 — excerpt
This initiation has varied greatly through the centuries according to circumstances. In the first centuries of the Church, Christian initiation saw considerable development. A long period of catechumenate included a series of preparatory rites, which were liturgical landmarks along the path of catechumenal preparation and culminated in the celebration of the sacraments of Christian initiation.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.