The are a number of old legends as to the origin of Sliab an Iarainn and Lough Allen.
According to one story two giants met where Lough Allen now stands and began to quarrel. Each of these giants carried a great enormous iron sword and after a while the swords broke into pieces and sank into the ground.
As the had no swords to fight with the threw "clabar" at each other thus forming Sliab an Iarainn and the Arigna mountains each of which iron is found.