Irenaeus has been called the most important witness of the Christianity of the 2nd century. Taught by Polycarp, who had been instructed by John the apostle, Irenaeus became Bishop of Lyon in 178. In his "Against the Heresies", Irenaeus wrote, "Although there are many dialects in the world, the force of the tradition is one and the same. For the same faith is held and handed down by the churches established in the German states, the Spains, among the Celtic tribes, in the East, in Libya, and in the central portions of the world." In Book 3, Irenaeus continues his defense of the unity of the church around the bishop, writing, "By pointing out the apostolic tradition and faith announced to mankind, which has been brought down to our time by successions of bishops, in the greatest, most ancient, and well known church, founded and established by the two most glorious apostles, Peter and Paul, at Rome, we can confound all who in any other way … gather more than they ought."