Ruis closes the third family of ogham with the maximum stroke count.
How the letter is formed
Ruis is the fifth letter of the third family, Aicme Muine, and is cut as five parallel strokes crossing the line obliquely. It is the most labour-intensive character in the system to cut, five strokes each carried across the arris and down both faces of the stone.
Five oblique strokes on a worn stone
A five-stroke oblique character is the single hardest letter in ogham to read on a damaged inscription. The strokes are long, they cross the edge that weathers first, and a lost stroke turns Ruis into Straif rather than into an obvious gap. Where a reading of an eroded stone is disputed, characters of this shape are often the disputed ones.
The sound
Ruis carries the value R, a common consonant in the personal names that make up almost the whole surviving corpus. Those inscriptions were cut on standing stones in Ireland and in Irish-settled parts of Wales, Scotland and the Isle of Man, and are dated on linguistic grounds to roughly the fourth to the sixth centuries.
The layers after the stones
The elder attached to this letter comes from the manuscript glosses, several centuries later. The seasonal and calendrical arrangements circulating today descend from a twentieth-century reworking of that material and are later again. This atlas records the epigraphic letter, the medieval gloss and the modern scheme as three distinct things, because collapsing them is the commonest error made about ogham.