Although the spirit of religious devotion and of orthodox belief is evident in many of the hundreds of lyrics which he composed, four only may be classed as hymns. Three of these are concerned with the theme of the Holy Cross, _Pange lingua, gloriosi proelium certaminis_, “Sing, my tongue, the glorious battle,” _Vexilla regis prodeunt_, “The banners of the king advance,” and _Crux benedicta nitet_, “Radiant is the blessed cross.” The fourth, _Tempora florigero rutilant distincta sereno_, “Season of luminous days, marked bright with the birth of the flowers,” is a Resurrection hymn.[9] It is impossible to indicate here the extraordinary influence which this group of hymns has exerted in the evolution of Christian hymnody, continuing in Gaul the tradition, as it were, which Hilary first established. The circumstances of their origin and their lasting values will be considered in connection with processional hymns in Chapter VI. (See Illustrative Hymns, II. _Vexilla regis prodeunt_, “The banners of the king advance.”) II. Metrical Forms The problem of metrical forms and the prosody of the earliest Latin hymns, in general, is a phase of the same problem affecting Latin poetry as a whole. The subject is both complicated and obscure, entangled with that of Latin rhetorical prose style, the transition from the quantitative accent of ancient classical poetry to the stress accent of medieval and modern verse and with the origin of rhyme. It is a problem for specialists among whom opinions are now divergent. Toward a practical understanding of the metrical values of the hymns of Hilary, Prudentius, Ambrose and Fortunatus, the pragmatic test of what is singable may be applied. The ancient balanced rhythms of Semitic poetry as illustrated in the Hebrew psalms had been sung for generations. The metrical lyrics of ancient Greece were sung to an instrumental accompaniment as were the Latin lyrics of the Golden Age of Rome. These highly polished classical forms were for the elite. Of popular poetry which was sung in the period immediately preceding the appearance of the Latin hymn, very little is known. The early writers were experimenters. Hilary used classical meters with alterations, of which the trochaic tetrameter catalectic proved most acceptable.[10] It is illustrated in _Adae carnis gloriosae_ and also in hymns by Prudentius and Fortunatus. Prudentius used a variety of meters in addition to the trochaic which proved adaptable in actual liturgical practice but by that time stress accent was beginning to obscure the original quantitative values. Ambrose used the unrhymed iambic dimeter, a simple and singable form which has been in vogue ever since, at first unrhymed after the original models and later rhymed. The popular trochaic meter familiarized by Hilary, Prudentius and Fortunatus, when transformed by stress accent and rhyme, is easily recognized both in Latin and the vernaculars.