The horizontal fraction bar was introduced by the Arabs. Several sources attribute the horizontal fraction bar to al-Hassar around 1200. The bar is generally found in Latin manuscripts of the late Middle Ages, but when printing was introduced it was frequently omitted, doubtless owing to typographical difficulties. Michael Closs points out that if we define a horizontal fraction bar to be a horizontal line that separates the numerator from the denominator and demarcates them as such, then this type of notation was used with exactly that purpose more than a millennium before al-Hassar. In problems 51 and 72 the denominator is underlined.
Some writers use the term vinculum for the horizontal fraction bar.
This term originally applied to the mark when used as a grouping symbol. Fibonacci used the Latin word virga for the horizontal fraction bar. This usage of the horizontal fraction bar was found by Hans Lausch, who believes there are likely even earlier occurrences. Lausch has also found the horizontal fraction bar in Allgemeine Deutsche Bibliothek, a Berlin review journal which was started in 1765. A precise reference may be forthcoming.