In the year 17 B.C. Augustus found an opportunity of testifying his regard for Horace. The secular games, which were celebrated in that year, included the singing of a hymn to Apollo and Diana by a chorus of 27 boys and the same number of girls, selected from the highest families in the state. The composition of this hymn was intrusted to Horace, much to his own legitimate pride, and to our instruction and pleasure, for not only is it a poem of high intrinsic excellence, but it is the only considerable extant specimen of the lyrical part of Roman worship. Some scholars include under it besides the _Carmen Saeculare_ proper, various other odes, some of which unquestionably bear on the same subject, though, there is no direct evidence of their having been sung together. [34] Whether Horace had any Roman models in this style before him is not very clear. We have seen that Livius Andronicus was selected to celebrate the victory of Sena, [35] and there is an ode of Catullus [36] which seems to refer to some similar occasion. Doubtless the main lines in which the composition moved were indicated by custom; but the treatment was left to the individual genius of the poet. In this case we observe the poet's happy choice of a metre. Of all the varied lyric rhythms none, at least to our ears, lends itself so readily to a musical setting as the Sapphic; and the many melodies attached to odes in this metre by the monks of the Middle Ages attest its special adaptability to choir-singing. Augustus was highly pleased with the poet's performance, and two years' afterwards he commanded him to celebrate the victory of his step-sons Drusus and Tiberius over the Rhaeti and Vindelici. [37] This circumstance turned his attention once more to lyric poetry, which for six years he had quite discontinued. [38] It is not conclusively proved that he wrote all the odes which compose the fourth book at this period; two or three bear the impress of an earlier date, and were doubtless improved by re-writing or revision, but the majority were the production of his later years, and present to us the fruits of his matured judgment and taste. They show no diminution of lyric power, but the reverse; nor is there any ode in the first three books which surpasses or even equals the fourth poem in this collection. Horace's attention was, during the last few years of his life, given chiefly to literary subjects; the treatise on poetry and the epistle to Julius Florus were written probably between 14 and 11 B.C. That to Augustus is the last composition that issued from his pen; we may refer it to 10 B.C. two years before his death.