A cathedral is a church that contains the cathedra, Greek for seat, of a bishop, thus serving as the central church of a diocese, conference or episcopate. The cited article says churches with the function of cathedral are usually specific to those Christian denominations with an episcopal hierarchy, such as the Catholic, Eastern Orthodox, Anglican and some Lutheran churches, and that church buildings embodying the functions of a cathedral first appeared in Italy, Gaul, Spain and North Africa in the fourth century, although cathedrals did not become universal within the Western Catholic Church until the twelfth century. Buildings recorded in the atlas as cathedrals are grouped under this concept.