One of the most common distortions you get in popular histories of religion is in the use of the term 'Roman Catholic Church'. We all think we know that this means. Coupled with the term 'Vatican' it means an ancient and all powerful organistation responsible for the corruption of Christianity, usually hand in hand with the Emperor Constantine.
It is true that the Nicene Creed refers to the 'Holy, catholic and apostolic church' but given both Protestants and Greek orthodox say the same words, we can be sure this does not mean the Roman Catholic Church. German Lutherans seem to be the one exception. I once attended evening song with a German at King's College Chapel in Cambridge where the Church of England service was according to Archbishop Cramner's words. The German was a Lutheran and rather surprised me by saying that at home, her church used the words 'Holy, Christian and Apostolic Church'. I don't know if it is true, but I do know that if it is, Luther will be rolling in his grave as he was quite certain that he was a true catholic even after the break from Rome.
So, 'Catholic' does not necessarily mean the Roman Catholic Church. By the later, we must mean the organisation of which the pope is the leader and which is based where the pope makes his court (usually in Rome but it has moved to Avignon in France). If you were reading the Da Vinci Code or many other popular books, you could be forgiven for thinking that the Roman Catholic Church enjoyed its power in the third and fourth centuries when Rome first converted to Christianity. Indeed, the Church itself likes us to believe this (I'm a Catholic too, but know better). In fact, the Popes have never had any authority over the Eastern Church and even though they declared themselves first among equals over the other patriarchs, this was a dead letter. But when the barbarians invaded the Western Roman Empire after 400AD, the Emperor, in Constantinople, found his writ no longer ran in the old western provinces and the Pope was left with a free hand. It was only in 496AD, when Clovis converted to Rome with his Franks, that the Pope's flock began to be significant.
All that stuff you hear about Constantine being in cahoots with the Roman Catholics and how the Council of Nicea was a Vatican plot are a load of rubbish. The Roman Catholics didn't even exist as a recognised group. 'Catholic' meant everybody who was an orthodox Christian, very few of whom looked to Rome. So, if you hear someone talking about the power of the Roman Catholics, the Pope or the Vatican before the late fifth century, you can be pretty sure they don't know what they are talking about.