From about the fourth century our knowledge of the Liturgy increases enormously. We are no longer dependent on casual references to it: we have definite rites fully developed. The more or less uniform type of Liturgy used everywhere before crystallized into four parent rites from which all others are derived. The four are the old Liturgies of Antioch, Alexandria, Rome, and Gaul. Each is described in a special article. It will be enough here to trace an outline of their general evolution. … Only Gaul and northwest Europe generally, though part of the Roman Patriarchate, kept its own rite till the seventh and eighth centuries.