The Catholic Church was founded by Jesus Christ. The New Testament records Jesus' activities and teaching, his appointment of the twelve Apostles, and his instructions to them to continue his work. The Catholic Church teaches that the coming of the Holy Spirit upon the apostles, in an event known as Pentecost, signalled the beginning of the public ministry of the Church. Catholics hold that Saint Peter was Rome's first bishop and the consecrator of Linus as its next bishop, thus starting the unbroken line which includes the current pontiff, Pope Francis. That is, the Catholic Church maintains the apostolic succession of the Bishop of Rome, the Pope – the successor to Saint Peter.
In the account of the Confession of Peter found in the Gospel of Matthew, it is believed that Christ designates Peter as the "rock" upon which Christ's church will be built. While some scholars do state Peter was the first Bishop of Rome, others say that the institution of the papacy is not dependent on the idea that Peter was Bishop of Rome or even on his ever having been in Rome. Many scholars hold that a church structure of plural presbyters/bishops persisted in Rome until the mid-2nd century when the structure of a single bishop and plural presbyters was adopted and that later writers retrospectively applied the term "bishop of Rome" to the most prominent members of the clergy in the earlier period and also to Peter himself. On this basis, Oscar Cullmann and Henry Chadwick question whether there was a formal link between Peter and the modern papacy, and Raymond E. Brown says that, while it is anachronistic to speak of Peter in terms of a local bishop of Rome, Christians of that period would have looked on Peter as having "roles that would contribute in an essential way to the development of the role of the papacy in the subsequent church". These roles, Brown says, "contributed enormously to seeing the bishop of Rome, the bishop of the city where Peter died, and where Paul witnessed to the truth of Christ, as the successor of Peter in care for the church universal".
An engraving of St Irenaeus, Bishop of Lugdunum in Gaul (now Lyon, France)
Four Marks of the Church
CATHOLIC The word “catholic ” means “universal,” in the sense of “according to the totality totality ” or “in keeping with the whole.” The Church is catholic in a double sense: First, the Church is catholic because Christ is present in her. “Where there is Christ Jesus, there is the Catholic Church.”307 In her subsists the fullness of Christ’s body united with its head; this implies that she receives from him “the fullness of the means of salvation”308 which he has willed: correct and complete confession of faith, full sacramental life, and ordained ministry in apostolic succession The Church was in this fundamental sense catholic on the day of 307 St. Ignatius of Antioch, Ad Smyrn. 8,2:Apostolic Fathers,II/2,311. 308 UR 3 Unitatis Reditegratio Decree on Ecumenism [11 /21 /1964] succession. The Church was, in this fundamental sense, catholic on the day of Pentecost309 and will always be so until the day of the Parousia. (CCC #830) UR 3 Unitatis Reditegratio Decree on Ecumenism [11 /21 /1964] Eph 1:22-23. 22And he put all things beneath his feet and gave him as head over all things to the church, 23which is his body, the fullness of the one who fills all things in every way. AG 6 Ad Gentes Vatican II, Decree on the Mission Activity of the Church [12/07/1965] 309 Cf. AG 4. Ad Gentes Vatican II, Decree on the Mission Activity of the Church [12/07/1965]
Secondly, the Church is catholic because s he has been sent out by Christ on a mission to the whole of the human race:310 All men are called to belong to the new People of God. This People, therefore, while remaining one and only one is to be spread throughout the whole world a while remaining one and only one, is to be spread throughout the whole world and to all ages in order that the design of God’s will may be fulfilled: he made human nature one in the beginning and has decreed that all his children who were scattered should be finally gathered together as one. ... The character of universality which adorns the People of God is a gift from the Lord himself whereby the Catholic Church ceaselessly and efficaciously seeks for the return of all humanity and all its goods, under Christ the Head in the unity of his Spirit.311 ( ) CCC #830) 310 Cf. Mt 28:19. 19Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, 20teaching them to observe all that I have commanded you. And behold, I am with you always, until the end of the age.” 311 LG 13 §§ 1-2 cf. Jn 11:52. 51He did not say this on his own, but since he was high priest for that year, he prophesied that Jesus was going to die for the nation 52 Jesus was going to die for the nation, and not only for the nation but also to gather into one the dispersed children of God.
Note Numbers are referring to the Catholic Catechism (CCC) and or the Holy Bible
Conditions in the Roman Empire facilitated the spread of new ideas. The empire's well-defined network of roads and waterways allowed easier travel, while the Pax Romana made it safe to travel from one region to another. The government had encouraged inhabitants, especially those in urban areas, to learn Greek, and the common language allowed ideas to be more easily expressed and understood. Jesus's apostles gained converts in Jewish communities around the Mediterranean Sea, and over 40 Christian communities had been established by 100. Although most of these were in the Roman Empire, notable Christian communities were also established in Armenia, Iran and along the Indian Malabar Coast. The new religion was most successful in urban areas, spreading first among slaves and people of low social standing, and then among aristocratic women.
At first, Christians continued to worship alongside Jewish believers, which historians refer to as Jewish Christianity, but within twenty years of Jesus's death, Sunday was regarded as the primary day of worship. As preachers such as Paul of Tarsus began converting Gentiles, Christianity began growing away from Jewish practices to establish itself as a separate religion, though the issue of Paul of Tarsus and Judaism is still debated today. To resolve doctrinal differences among the competing factions, sometime around the year 50 the apostles convened the first Church council, the Council of Jerusalem. This council affirmed that Gentiles could become Christians without adopting all of the Mosaic Law. Growing tensions soon led to a starker separation that was virtually complete by the time Christians refused to join in the Bar Kokhba Jewish revolt of 132, however some groups of Christians retained elements of Jewish practice.
According to some historians and scholars, the early Christian Church was very loosely organized, resulting in diverse interpretations of Christian beliefs. In part to ensure greater consistency in their teachings, by the end of the 2nd century Christian communities had evolved a more structured hierarchy, with a central bishop having authority over the clergy in his city leading to the development of the Metropolitan bishop. The organization of the Church began to mimic that of the Empire; bishops in politically important cities exerted greater authority over bishops in nearby cities. The churches in Antioch, Alexandria, and Rome held the highest positions. Beginning in the 2nd century, bishops often congregated in regional synods to resolve doctrinal and policy issues. Duffy claims that by the 3rd century, the bishop of Rome began to act as a court of appeals for problems that other bishops could not resolve.
The Doctrine was further refined by a series of influential theologians and teachers, known collectively as the Church Fathers. From the year 100 onward, proto-orthodox teachers like Ignatius of Antioch and Irenaeus defined Catholic teaching in stark opposition to other things, such as Gnosticism. Teachings and traditions were consolidated under the influence of theological apologists such as Pope Clement I, Justin Martyr, and Augustine of Hippo.