The church from its birth appears to us as a growing phenomenon of aggregation to the initial group through the work of the apostles Acts 2:41-47; 5:14; 11:24; 17:4; the number of communities in different cities grows, but all were in communion with each other through their origin and their profession of faith. Tertullian expressed this common doctrine as follows: â€œSo the apostles which means â€˜sentâ€™ at first preached faith in Jesus Christ and set up churches for Judea and, soon after, scattered throughout the world, announced the same doctrine and the same faith to the nations and so founded churches in every city. From these the other churches then derived the offshoots of their faith and the seed of doctrine, and still derive it in order to be churches. In this way they too are considered apostolic, as offspring of the churches of the apostlesâ€ De praesc. 20,4-7. To this end we see, from the start, the apostles bringing into being certain structures that would ensure continuity for their teaching and ministry: they set up leaders Acts 14:23; 20:17-35; 1 Tim 4:14; 2 Tim 1:6, who were to do the same Tit 1:5-9; 2:1-15; 1 Tim 5:17-22. On the one hand, there was the idea of a doctrine to be jealously guarded 1 Tim 4:12-16; 6:20; 2 Tim 1:13-14; 2:15; 3:14â€“4:5; on the other, the idea of continuity of ministry through the legitimate succession of the communityâ€™s leaders Clem. Rom., Ep. ad Cor., chs. 42 and 44. This idea, already present in Clement of Rome, is developed in Irenaeus, who writes: eos qui ab apostolis instituti sunt episcopi et successores eorum usque ad nos Adv. haer. III, 3,1; cf. III, 3,4; IV, 26,2, and reaches its full formulation with Hippolytus and Tertullian.