The clàrsach is a Gaelic triangular, wire-strung harp.
This type of harp has always been known by the feminine term cruit but by 1204 was certainly known by the masculine term 'clàr' (board) and, by the 14th century, by the feminine form of 'clàr', i.e., 'clàirseach/clàrsach'. (Gd.)
The origins of the Gaelic triangular harp go back at least to the first millennium. There are several stone carvings of triangular harps from the 10th century, many of which have simple triangular shapes, generally with straight pillars, straight string arms or necks, and soundboxes. There is stone carving evidence that the lyre or non-triangular harp were present in Ireland during the first millennium. Evidence for the triangular harp in Pictish Scotland dates from the 9th century.
The clàrsach or harp was the most popular musical instrument in later medieval Scotland and Ireland and Gaelic poets portrayed their Pictish counterparts as very much like themselves.
Scotland, because of her affinity and intercourse [with Ireland], tries to imitate Ireland in music and strives in emulation. Ireland uses and delights in two instruments only, the harp namely, and the tympanum. Scotland uses three, the harp, the tympanum and the crowd. In the opinion, however, of many, Scotland has by now not only caught up on Ireland, her instructor, but already far outdistances her and excels her in musical skill. Therefore, [Irish] people now look to that country as the fountain of the art.
The clàrsach played by the Gaels of Scotland and Ireland between the 11th and 19th centuries was certainly wire-strung. The Irish Maedoc book shrine dates from the 11th century, and clearly shows a harper with a triangular framed harp including a "T-Section" in the pillar. The Irish word lamhchrann or Scottish Gaelic làmh-chrann came into use at an unknown date to indicate this pillar which would have supplied the bracing to withstand the tension of a wire-strung harp.
The Irish and Highland Harps by Robert Bruce Armstrong describes these ancient harps. There is historical evidence that the types of wire used in these harps are iron, brass, silver, and gold. Three pre-16th-century examples survive today; the Brian Boru Harp in Trinity College, Dublin, and the Queen Mary and Lamont Harps, both in Scotland.