§ Of the Coming of the Elves and the Captivity of Melkor The Silmarillion

Melkor met the onset of the Valar in the North-west of Middle-earth, and all that region was much broken. But the first victory of the hosts of the West was swift, and the servants of Melkor fled before them to Utumno. Then the Valar passed over Middle-earth, and they set a guard over Cuiviénen; and thereafter the Quendi knew nothing of the great Battle of the Powers, save that the Earth shook and groaned beneath them, and the waters were moved, and in the north there were lights as of mighty fires. Long and grievous was the siege of Utumno, and many battles were fought before its gates of which naught but the rumour is known to the Elves. In that time the shape of Middle-earth was changed, and the Great Sea that sundered it from Aman grew wide and deep; and it broke in upon the coasts and made a deep gulf to the southward. Many lesser bays were made between the Great Gulf and Helcaraxë far in the north, where Middle-earth and Aman came nigh together. Of these the Bay of Balar was the chief; and into it the mighty river Sirion flowed down from the new-raised highlands northwards: Dorthonion, and the mountains about Hithlum. The lands of the far north were all made desolate in those days; for there Utumno was delved exceeding deep, and its pits were filled with fires and with great hosts of the servants of Melkor.