Tlachtga was the daughter of the druid Mug Ruith according to Irish tradition. She accompanied him on his world travels, learning his magical secrets and discovering sacred stones in Italy. She was raped by the three sons of Simon Magus, her father's mentor, and returned to Ireland where she gave birth to triplets called Cumma, Doirb et Muach issued from 3 different fathers. They were born on the hill that would bear the name of their mother. The triple birth is a common theme in Celtic mythology, and her death of grief and the construction of a fortress at her grave echoes the story of Macha.
The Hill of Tlachtga is associated with the Hill of Ward in County Meath, and its celebrations rivaled those at Tailtiu. The major ceremony held at Tlachtga was the lighting of the winter fires at Samhain (November 1). The ringfort built on the hill was associated not only with the kings of Mide, but also with Munster as well. The site was known in the popular culture of medieval Ireland as a place where Mug Ruith's flying machine roth rámach had been seen, and where the ard rí Ruaidrí Ua Conchobair had held a massive assemblage in 1168.
- James MacKillop (1998). Dictionary of Celtic Mythology. London: Oxford. ISBN 0-19-860967-1.