A ligature is a coherent graphical symbol that represents at least two
distinct notes. Ligatures originally appeared in the manuscripts of
Gregorian chant notation roughly since the 9th century to denote
ascending or descending sequences of notes. In early notation,
ligatures were used for monophonic tunes (Gregorian chant) and very
soon denoted also the way of performance in the sense of articulation.
With the invention of the metric system of the white mensural
notation, the need for ligatures to denote such patterns disappeared.