Originally it was. However, with the veneration of Mary, the collection of idols ( holy objects ), and the praying to the dead, it slipped into a quasi pagan state which allowed for inclusion of the remaining stalwart Roman pagans to join in. In fact some of the Saints have similar qualities and even images to Pagan Gods. The truth is it is a religion without any life. Jesus said that repetition and tradition is meaningless. All Roman Catholics do is tradition and repeated prayers. So in close. Yes they were Christians, Yes they are now what we call a denomination. But no, they are not Christians, they are Catholics.