The complete collection of liturgical chants upon which Rome finally set her approval has been called for ages the _Antiphonarium Romanum_; and this, as Rome became the head of the organization of the church, was adopted by all other branches in Western Europe as the Bible, so to speak, of ecclesiastical song. It was compiled from four collections of which the Ambrosian was one, the others being the Gregorian, the Gallican, and the Mozarabian or Spanish. The principal manuscripts in these collections have been reproduced in facsimile by the Benedictine monks of Solesmes in their invaluable _Paléographie musicale_ (1889 _et seq._). To quote from the introduction to this magnificent series: 'The Gregorian, Ambrosian, Mozarabian, and the little which remains to us of the Gallican _dialects_, seem in fact to have one common source, to have been derived from the same musical language: the chant of the Latin church in its cradle. That is at least the opinion to which we have been brought by the examination of the manuscripts in the libraries of our own monasteries and of those which we have been able to consult elsewhere. Concerning the similarities we can say modes and rhythms are the same in the four varieties of chant. The melodic forms present the same general character.... Moreover, in these diverse musical dialects certain melodic types or airs constantly recur which are always perfectly recognizable, in spite of the differences resulting from the peculiarities of style or character proper to each of them. Among the Ambrosian and Gregorian these mutual borrowings, these common heritages are especially frequent.’ The history of these collections is extremely obscure. No manuscripts are extant of earlier date than the twelfth century. As to who actually compiled the _Antiphonarium Romanum_, a long-standing and generally accepted tradition ascribed it to St. Gregory the Great (d. 604), but the validity of the tradition has been attacked by a number of reputable and authoritative modern historians, conspicuous among whom is Gevaert. Without entering into the merits of the controversy we shall briefly indicate the earliest sources of information on liturgical collections, following Gevaert on the Gregorian tradition, not in _parti pris_, but because the tradition has been so long and so strongly intrenched that it is more in need of examination than of support.