§ Of the Rings of Power and the Third Age The Silmarillion

And in the days of Eärnil they made their first stroke, and they came by night out of Mordor over the passes of the Mountains of Shadow, and took Minas Ithil for their abode; and they made it a place of such dread that none dared to look upon it. Thereafter it was called Minas Morgul, the Tower of Sorcery; and Minas Morgul was ever at war with Minas Anor in the west. Then Osgiliath, which in the waning of the people had long been deserted, became a place of ruins and a city of ghosts. But Minas Anor endured, and it was named anew Minas Tirith, the Tower of Guard; for there the kings caused to be built in the citadel a white tower, very tall and fair, and its eye was upon many lands. Proud still and strong was that city, and in it the White Tree still flowered for a while before the house of the Kings; and there the remnant of the Númenóreans still defended the passage of the River against the terrors of Minas Morgul and against all the enemies of the West, Orcs and monsters and evil Men; and thus the lands behind them, west of Anduin, were protected from war and destruction.