The One Church on earth
When we say that we believe in One Church what we mean is that Jesus founded One Church, not two or three, and that there is One Church and one only today. Let us think now of the history of the Church as of a river flowing on through the centuries.
Founded by Our Lord
The Church was founded by Jesus in Jerusalem with the 12 Apostles as its first members. This was around the year 30 AD. So, thinking of the history of the Church as the course of a river, we know that the source of the river, its beginning, was Our Lord himself.
At that time the lands round the Mediterranean were ruled by the Romans. This was the mighty Roman Empire, and it stretched from Palestine to Britain. As the Church spread, so bishops were appointed to be in charge of the Church in the various cities and towns. The capital and the centre of the Empire was the city of Rome in Italy, where St Peter and St Paul were martyred, and the Bishop of Rome, who was also called the Pope or Father of Rome, was the chief bishop in the Church.
The Great Schism
During the course of the centuries the Church at the eastern end of the Mediterranean lands got rather out of touch with the Church in the West; and in 1054, as a result of a number of disputes, there was a separation between the two. The result was that the Church was now divided into the Western Church, which remained under the Pope, and the Eastern Church. So we can think of the river forking at this point.