This is a story from the Lebor Gabala Erenn, The Book of Invasions, which are myths of the early Celtic settlers of Ireland.
Dagda, the good god, was the father god of the Celts and the king of the fairy race of Tuatha de Danann who moved to Ireland. When they came across the waters, they brought with them many magical gifts. Among them was a cauldron called Undry that provided unlimited food and had the power to restore life.
Another was a harp called Uaithne, which could cause seasons to change and played three types of music. This magic harp was made of oak and was decorated with precious jewels. However, it was only Dagda who could play this harp with all it enchantments.
Dagda carried the harp with him everywhere, even to battle. Those were the days of war and the golden-haired, blue-eyed Tuatha de Danaan were battling the Formorians who had long, dark-hair and darker eyes.
As his men readied themselves for war, Dagda would set up his harp and run his finger gently across the strings and magically, a war song would begin to play. To that, the men would buckle their armours and go marching out to face the enemy, spears in hand shouting: ‘Forth the fight.’
At the end of the battle, when the wounded and weary warriors returned, Dagda would, with a sweep of his hand, cause the harp to play again. This time it was a soothing tune; the men no longer felt the pain of their wounds and their thoughts would be only of the honours they had won and the safety of their kin.
During the second battle of Moytura, the Formorians heard about Dagda’s magic harp and decided to steal it. So, while the battle was still going on, some of the Formorian warriors crept into the hall of the Tuatha de Danaan, stole the harp and fled to the country along with their women and children. Soon the rest of their people, who suffered a bitter defeat at the hands of Dagda’s men, had to beat a hasty retreat too.
When Dagda returned to the camp and called for his harp as usual, he found it missing. ‘No doubt, it is the evil Formorians who have stolen my harp! As if it’s going to listen to them! I’ll go teach them a lesson they’ll never forget in a hurry and get it back.’ He was very, very angry! Two of his best warriors, Ogma and Lugh, offered to go with him to retrieve Uaithne.
The three of them travelled far, searching for the Formorians. Before long, they came upon the enemy who had taken shelter in an abandoned castle. As they approached, they could hear loud laughter and merrymaking as the group wined and dined in the great hall. As he entered the hall, Dagda could see his harp hanging on the wall in the dim light of the candles.
‘Time to play,’ whispered Lugh in his ear and very softly, Dagda began to chant:
‘Come Daurdabla, apple-sweet murmurer,
Come, Coir-cethair-chuir, four-angled frame of harmony,
Come summer, come winter,
Out of the mouths of harps and bags and pipes!’
Instantly, the harp moved across the hall to his waiting arms, knocking down dead nine people on its way! The Formorians were shocked into silence.
As Dagda brushed his fingers across the strings, the harp began to play by itself. First came the goltrai, the music of tears, and mournful strains filled the room. Women, children and even the men began to weep and lament their defeat. Next, the harp began playing the geantrai, the music of merriment, and the crowd roared with laughter. As they laughed, the soldiers dropped their spears and broke their wine goblets, which fell from their hands.
Slowly, the harp changed its tune. It was time for the music of slumber, the suantrai. The notes fell soft as snow and gentle as a summer breeze. Children slowly clambered on to their mothers’ laps and feel asleep in that comforting warmth. The women could hardly keep their eyes open and were soon nodding off to sleep. Before long, the menfolk, old and young, were drooping over their seats as sleep overcame them.
As the Formorians slept, Dagda and his men quietly left as they had come, having retrieved the magic harp.