The madrigal is a form of secular vocal music, that arose in Italy during the early 16th century. It differed from most of the strophic musical forms of the time in that it was fully written out, with the composer attempting to convey the emotions contained in each line of poem though the use of musical resources. Madrigals are traditionally written for three to eight voices, and initially they were without accompaniment. Claudio Monteverdi wrote nine books of madrigals which not only define the form, but also experiment with it: he wrote madrigals with solo parts for voice, accompanied by continuo, including recitative passages and foreshadowing the eventual absorption of the solo madrigal into the aria. During the early 1600's, the madrigal ceased to be a purely a capella composition. Composers included instrumental lines, continuo accompaniment, and a progressive exaltation of the importance of the soprano and bass lines, which was in line with the rise of functional tonality.