Knowledge of and belief in the principles of the Faith as contained in the Creed (symbolum) have of course always been required before Baptism from very early times. Leo here calls catechumens regenerandi, just as those who are being baptized are spoken of as renascentes (e.g. Lett. XVII. 8), those who have been baptized as renati (passim), and the rite itself as sacramentum regenerationis (e.g. Lett. IX. 2).