Long ago there was a Breton king by the name of Gradlon who ruled over Ys, a seaside kingdom that was protected from the sea by a dyke, to whose sluices only he had the keys. His daughter whose  name was Ahes, !ed a life of debauchery and was one day seduced by the devil who required, as a token of her love, to open the sluices. This Ahes did, having stolen the keys from her father The town of Ys was washed away and Gradlon the King,
took flight upon his horse grabbing the errant Princess Ahes as he went. A voice from the sky told him to drop her in the water. This he did, and in so doing Ahes was condemned to entice and lure sailors to her kingdom under the sea. 
The ancient story of Ys is eloquent of the fear of the power of women by the patriarchal order and the domination of the Christian church.

What is celtic music?

The term 'celtic music' is a rather loose one;, it covers the traditional music of the celtic countries - Ireland, Scotland, Wales, Brittany (in France) - where celtic languages were and still are spoken - and Galicia (in Spain) 

But the term is sometimes controversial. For starters, the ancient Celts as an identifiable people are long gone, also there are strong differences between traditional music in the different countries, and many of the similarities are due to more recent influences. There is as well the notion that 'celtic' implies celtic mysticism which is a strong influence in new age music although very often the music itself  has little to do with traditional music. This confusion is easily explained because myths and legends are a very important feature of traditional celtic music. 
In Canada and the US, the traditions are much more mixed, and it is there that the term 'celtic' is most used, though it is also true that many groups from particular celtic regions play the music of another region too. 

A pond in the forest of Broceliande in Brittany associated with the legend of Merlin
 
 

CELTIC MUSIC IN BRITTANY

In 'Basse Bretagne', the western part of Brittany,  traditionally, since at least the middle of the 18th century, for every social occasion when music was needed - and there were numerous excuses for a dance ! - two 'sonneurs' (pipe players), one playing the bombarde (a kind of soprano  oboe) and the other the biniou (the high pitched bagpipe native to Brittany) took charge with sometimes the help of a tambourine player. (on the picture the bombarde is on the left).
The music played like most traditional music all over the world was monodic : the two instruments playing the same melody one octave apart or in unison. The melodies are modal with the predominance of the aeolian and the myxolydian modes but also the dorian, phrygian and several pentatonic modes are also widely used.* Dances rhythm are generally regular in 4/4 or 12/8.      Two Breton musicians photographed around 1900

But music also was very much used by story tellers and there is a huge repertoire of gwerz ( melodies) with rhythms much more fluid and irregular.
 
 

Soon after the Second World War where the traditional way of life was quickly fading away after years of decline - in 1942 there were only 17 players left - a renaissance of traditional music started thanks to the association  Bodadeg ar Sonerion (The Pipers Gathering). Their work was three fold: collecting song, teaching the instrumental practice and finding new ways to use the old material. In 1948 was created the first bagad (marching band) borrowing from the Scottish pipe band the drums and the highland bagpipes along side the native bombardes, an innovation which was extraordinarily successful: nowadays there is not a town or  a public organization which has not a bagad at hand - up to the point that most people think this is the original orchestral format of Breton music !
On the classical side seminal developments also took place notably in church music where old Breton hymns were harmonized for choirs or for bombarde and organ. Thus a very popular new repertoire was created.

At the end of the sixties new developments took place in Brittany, this time in parallel with the folk rock explosion in Britain and the USA The contribution of Alan Stivell is outstanding: he created or recreated a completely new repertoire for the harp in Brittany (his father invented a new Celtic harp based on middle ages and Irish models) Alan Stivell's band (with Dan Ar Bras on electric guitar) was enormously successful (1 500 000 copies sold in France of Live at the Olympia) giving back to people in Brittany their pride and faith in their own culture.

For a while, in the eighties, celtic music went out of fashion, but, still a growing number of musicians went on experimenting and honing their skills. Now this music is more popular than ever. New combinations appear all the time with new techniques, rhythms - like rap, techno, rai, world music  - new instruments like synthesizers, computers, samplers drum machines and this alongside more traditional instruments from all over the world.
 * On a piano keyboard, the aeolian mode is a serie of notes starting on A and ending on A one octave higher using only the white keys (e.g. A.B.C.D.E,F,G.A). The myxolydian mode starts on G and ends with G, dorian (D) and phrygian (E). Pentatonic modes are five note scales.