§ Of the Coming of Men into the West The Silmarillion

The Edain did not long dwell content in Estolad, for many still desired to go westward; but they did not know the way. Before them lay the fences of Doriath, and southward lay Sirion and its impassable fens. Therefore the kings of the three houses of the Noldor, seeing hope of strength in the sons of Men, sent word that any of the Edain that wished might remove and come to dwell among their people. In this way the migration of the Edain began: at first little by little, but later in families and kindreds, they arose and left Estolad, until after some fifty years many thousands had entered the lands of the Kings. Most of these took the long road northwards, until the ways became well known to them. The people of Bëor came to Dorthonion and dwelt in lands ruled by the house of Finarfin. The people of Aradan (for Marach his father remained in Estolad until his death) for the most part went on westward; and some came to Hithlum, but Magor son of Aradan and many of the people passed down Sirion into Beleriand and dwelt a while in the vales of the southern slopes of Ered Wethrin.