The oldest manuscripts of Gregorian chants were written using a graphic notation which uses a repertoire of specific signs called [[neume]]s; each neume designates a basic musical gesture (see [[musical notation]]). As books, made of [[vellum]] (prepared sheepskins), were very expensive, the text was abbreviated wherever possible, with the neumes written over the text. This was a notation without lines and no exact melodic contour could be deciphered from it, which implies that the repertoire was learnt by rote. In later stadia, the neumes are written onto staves of one or more lines; by the 11th century this had evolved into square notation, from which eventually the modern [[staff (music)|five-line staff]] developed in the 16th century.<ref>Development of notation styles is discussed at [http://www.dolmetsch.com/musictheory2.htm Dolmetsch online], accessed 4&nbsp;July&nbsp;2006</ref> As the dominating musical tradition throughout Europe, Gregorian chant became the root of all subsequent musical developments in Western music, beginning with the rise of [[polyphony]] in the 11th century.