Lludd and Llefelys
In early Welsh mythology, Llefelys was wise king of France whose brother Lludd ruled Britain. When Lludd's kingdom was beset by a number of menaces he enlisted the help of his brother.
Three things were plaguing Lludd: a demonic tribe called the Coraniaid; vanishing provisions from the king's court; and a recurring scream which struck fear into Lludd's people, causing women to miscarry and making animals and plants barren.
Llefelys decreed that a potion of crushed insects and water would destroy the Coraniaid. The wizard who had been stealing provisions was overcome and became subservient to Lludd. The scream was revealed to be the sound of two dragons fighting.
Llefelys told Lludd to dig a pit in the centre of Britain, fill it with mead and cover it with cloth. Lludd did this, and the dragons were imprisoned, wrapped in the cloth, underground at Dinas Emrys in North West Wales.