§ Of Beleriand and Its Realms The Silmarillion

Upon the left hand of Sirion lay East Beleriand, at its widest a hundred leagues from Sirion to Gelion and the borders of Ossiriand; and first, between Sirion and Mindeb, lay the empty land of Dimbar under the peaks of the Crissaegrim, abode of eagles. Between Mindeb and the upper waters of Esgalduin lay the no-land of Nan Dungortheb; and that region was filled with fear, for upon its one side the power of Melian fenced the north march of Doriath, but upon the other side the sheer precipices of Ered Gorgoroth, Mountains of Terror, fell down from high Dorthonion. Thither, as was earlier told, Ungoliant had fled from the whips of the Balrogs, and there she dwelt a while, filling the ravines with her deadly gloom, and there still, when she had passed away, her foul offspring lurked and wove their evil nets; and the thin waters that spilled from Ered Gorgoroth were defiled, and perilous to drink, for the hearts of those that tasted them were filled with shadows of madness and despair. All living things else shunned that land, and the Noldor would pass through Nan Dungortheb only at great need, by paths near to the borders of Doriath and furthest from the haunted hills. That way was made long before, in the time ere Morgoth returned to Middle-earth; and if one fared upon it he came eastwards to Esgalduin, where still there stood in the days of the Siege the stone bridge of Iant Taur. Thence he passed through Dor Dínen, the Silent Land, and crossing the Arossiach (which signifies the Fords of Aros) came to the north marches of Beleriand, where dwelt the sons of Fëanor.