One of the reasons, however, which no doubt has been most apt to suggest anterior compositions is the singular completeness of form exhibited by these poems. It is now practically agreed that--scraps and fragments themselves excepted--we have no monument of French in accomplished profane literature more ancient than the _Chanson de Roland_.[20] And the form of this, though from one point of view it may be called rude and simple, is of remarkable perfection in its own way. The poem is written in decasyllabic iambic lines with a caesura at the second foot, these lines being written with a precision which French indeed never afterwards lost, but which English did not attain till Chaucer's day, and then lost again for more than another century. Further, the grouping and finishing of these lines is not less remarkable, and is even more distinctive than their internal construction. They are not blank; they are not in couplets; they are not in equal stanzas; and they are not (in the earliest examples, such as _Roland_) regularly rhymed. But they are arranged in batches (called in French _laisses_ or _tirades_) of no certain number, but varying from one to several score, each of which derives unity from an _assonance_--that is to say, a vowel-rhyme, the consonants of the final syllable varying at discretion. This assonance, which appears to have been common to all Romance tongues in their early stages, disappeared before very long from French, though it continued in Spanish, and is indeed the most distinguishing point of the prosody of that language. Very early in the _chansons_ themselves we find it replaced by rhyme, which, however, remains the same for the whole of the _laisse_, no matter how long it is. By degrees, also, the ten-syllabled line (which in some examples has an octosyllabic tail-line not assonanced at the end of every _laisse_) gave way in its turn to the victorious Alexandrine. But the mechanism of the _chanson_ admitted no further extensions than the substitution of rhyme for assonance, and of twelve-syllabled lines for ten-syllabled. In all other respects it remained rigidly the same from the eleventh century to the fourteenth, and in the very latest examples of such poems, as _Hugues Capet_ and _Baudouin de Seboure_--full as enthusiasts like M. Gautier complain that they are of a spirit very different from that of the older _chansons_--there is not the slightest change in form; while certain peculiarities of stock phrase and "epic repetition" are jealously preserved. The immense single-rhymed _laisses_, sometimes extending to several pages of verse, still roll rhyme after rhyme with the same sound upon the ear. The common form generally remains; and though the adventures are considerably varied, they still retain a certain general impress of the earlier scheme.