Along with the invention and development of opera, during the period here mentioned, the mastery of the violin was carried forward with great results to the art of music. About 1685, Archangelo Corelli published his first collection of pieces for the violin, and in these are found what are practically about the first examples of a well-developed lyric melody, of the kind we now mean when we speak of "bel canto"--the type of melody made the very crux of the art of Italian singing. This impassioned, sustained, and expressive melody took with wonderful rapidity and was almost immediately adopted into opera, the ideal of which in the beginning had been that of an artistic and dramatically expressive delivery of the text. Now, melody as such has little to do with the dramatic delivery of the text. In a sustained melody--as in "Home, Sweet Home," to quote a simple type--it is first of all a question of sustained sentiment; whereas in a well-determined declamation it is first of all a matter of effective delivery of the words and phrases from an elocutionary standpoint, allowing the voice all the stops, interruptions, shocks, and variations of intensity requisite for effective delivery. But by the time this sustained melody had been introduced into high art (it seems to have made a beginning earlier in folk-song, although we have no precise indications upon the subject) the mere delivery of a text, somewhat after the manner of a liturgical intoning, no longer satisfied the demands of opera.
Music grew by what it fed upon. The violin, which Monteverde had placed in the position of honor at the head of the orchestra in 1608, had grown upon the ears of the people; and there was a need felt for something more impassioned, but at the same time more distinctively musical, than the mere declamation of the first opera, no matter how sing-song that delivery might be made. Hence arose the aria, which practically is a prolongation of a single moment of the dramatic situation. The Arias, at first and for quite a long time later, had very few words, and these were repeated over and over, as we find still in the well-known arias from Händel's "Messiah." Thus opera came into possession of a simple and sustained melody, patterned after the cantilena of the violin; and it was employed for marking the successive points of the dramatic action. That is to say, as the drama unfolded, one new situation after another developed itself. Each new entrance of a dramatic person made a new complication and a new situation, brought to the attention of the hearer by means of the lines and then enforced by the aria, which the singer of greatest momentary importance had to sing. That these arias very soon degenerated into show pieces for virtuoso singers was an accident due to the popularity of the operatic stage, the development of the new art of singing, and a delight in the human voice as a musical instrument. It has no concern with our present subject.