§ Of Túrin Turambar The Silmarillion

They came upon Morwen by the banks of Sirion, and Mablung besought her to return to Menegroth; but she was fey, and would not be persuaded. Then also the coming of Nienor was revealed, and despite Morwen's command she would not go back; and Mablung perforce brought them to the hidden ferries at the Meres of Twilight, and they passed over Sirion. And after three days' journeying they came to Amon Ethir, the Hill of Spies, that long ago Felagund had caused to be raised with great labour, a league before the doors of Nargothrond. There Mablung set a guard of riders about Morwen and her daughter, and forbade them to go further. But he, seeing from the hill no sign of any enemy, went down with his scouts to the Narog, as stealthily as they could go.