For the evolution of the processional hymn from this point to the close of the Middle Ages, we have in addition to hymnic manuscripts, the service books and manuals devoted to, or including, processional practice. The _Ritual_ or _Roman Pontifical_ was the earliest to include directions for processions, an illustration of which has been presented above in the case of _Sancta Maria, quid est?_ In the course of time, since so many medieval processions were not thus provided for, the _Processional_ came into existence, containing the order of processions for a particular diocese or monastery.[27] The St. Gall _Processionals_, for instance, are informative as to customs already described above. The specific name _versus_ gave rise to the title _Versarius_ for a book of processional hymns.[28] In addition to the collections, liturgical writers discussed the procession. Of these, none was more influential than Durandus, Bishop of Mende, who, about 1286, produced his _Rationale divinorum officiorum_ which among many other liturgical subjects, included processional rites.[29] Durandus was a leading authority upon ecclesiastical symbolism. Accordingly, he dwells upon every minute detail of the great processions for Easter, Ascension, Palm Sunday and the Purification as well as the Sunday procession and others of lesser importance, ascribing to each act a wealth of symbolic meaning. Much of this figurative interpretation is obvious and inherent in the feast to be celebrated but in other cases he gives full play to his sense of the symbolic, a phase of contemporary thought already so characteristic of Adam of St. Victor and other writers on religious themes. Finally he declares that whatever else is suggested, “the true procession is a progress to the celestial country.” (_Ipsa vero processio, est via ad coelestem patriam._)[30] If the fundamental concepts which entered into their origins be reviewed, medieval processions apparently carried with them the familiar ideas of supplication, of dramatic representation or of pilgrimage to sacred places. Durandus reiterates and sublimates these concepts, giving them an added significance.