Danú, whose own name means 'water', was the Earth Mother of the Iron Age Celts. Her husband was Lugh, the Celtic Sun God, who drove his chariot, pulled by fiery horses, across the sky each day from east to west.
Lugh and Danú represent the three basic elements which, together with air, are required for human survival.
It's an expression of the enduring strength of water, earth and fire. And it invokes the power of the Sun God.