Chaucer uses the same meter throughout almost all of his tales, with the exception of "Sir Thopas" and his prose tales. It is a decasyllable line, probably borrowed from French and Italian forms, with riding rhyme and, occasionally, a caesura in the middle of a line. His meter would later develop into the heroic meter of the 15th and 16th centuries and is an ancestor of iambic pentameter. He avoids allowing couplets to become too prominent in the poem, and four of the tales (the Man of Law's, Clerk's, Prioress', and Second Nun's) use rhyme royal.