The Nicene creed contains the line:
....he was crucified for us under Pontius Pilate, and suffered, and was buried, and the third day he rose again, according to the Scriptures, and ascended into heaven, and sitteth on the right hand of the Father;
There are slight variations between the Creed of the Council of Nicaea (325AD) and the Creed of the Council of Constantinople (381AD) but this portion remains substantively identical.
The Creed is given high importance in the Eastern Orthodox Church, Assyrian Church of the East, Oriental Orthodox churches, the Roman Catholic Church, including the Eastern Catholic Churches, the Old Catholic Church, the Lutheran Church, the Anglican Communion, and almost all branches of Protestantism, including the Reformed churches, the Presbyterian Church, and the Methodist Church.
I'd say that pretty conclusively proves that Catholics are Christians, wouldn't you ?