About the same time, or even in the first half of the thirteenth century, one of the many strictly-balanced forms of metre, in which Europe was then so fruitful, became a normal and recognised form in Italy--the sonnet. The order of rhymes and even the number of the lines varied for a whole century,[710] till Petrarch fixed them permanently. In this form all higher lyrical or meditative subjects, and at a later time subjects of every possible description, were treated, and the madrigals, the sestine, and even the ‘Canzoni’ were reduced to a subordinate place. Later Italian writers complain, half jestingly, half resentfully, of this inevitable mould, this Procrustean bed, to which they were compelled to make their thoughts and feelings fit. Others were, and still are, quite satisfied with this particular form of verse, which they freely use to express any personal reminiscence or idle sing-song without necessity or serious purpose. For which reason there are many more bad or insignificant sonnets than good ones. Nevertheless, the sonnet must be held to have been an unspeakable blessing for Italian poetry. The clearness and beauty of its structure, the invitation it gave to elevate the thought in the second and more rapidly moving half, and the ease with which it could be learned by heart, made it valued even by the greatest masters. In fact, they would not have kept it in use down to our own century, had they not been penetrated with a sense of its singular worth. These masters could have given us the same thoughts in other and wholly different forms. But when once they had made the sonnet the normal type of lyrical poetry, many other writers of great, if not the highest, gifts, who otherwise would have lost themselves in a sea of diffusiveness, were forced to concentrate their feelings. The sonnet became for Italian literature a condenser of thoughts and emotions such as was possessed by the poetry of no other modern people.