Nine:
A very powerful odd number for luck and magic; being 3x3 it multiplies the force of three and it is the number of months of pregnancy. Many curative charms, divinations and other magical procedures require words or actions to be repeated nine times, nine objects gathered, etc.

Nine Maidens.
Several groups of standing stones in Cornwall and Devon are called 'The Nine Maidens' or 'The Merry Maidens'. Supposedly, these were girls who were turned to stone for dancing on a Sunday; at Belsone, Devon, the piper was petrified too and the stones are said to dance every day at noon.
Such tales are pan-European; they date from the Middle Ages to warn of judgements on sinners who disregard holy times or places.

Both from - A Dictionary of English Folklore, Simpson and Roud.
Jim Carroll