In the War of the Elves and Sauron in the Second Age, the Dark Lord's forces overran the lands of Eriador, and Sauron threatened to conquer all of Middle-earth. High King Gil-galad sent to Númenor for help, and Tar-Minastir responded by sending an immense fleet to the aid of the Elves.
The Númenórean fleet was led by the great admiral Ciryatur, who cunningly divided his forces, sending some into the south while his main fleet landed in Lindon. Ciryatur's Númenórean warriors proved more than equal to Sauron's armies, and forced them southwards out of Eriador. At the decisive Battle of Gwathló Sauron was trapped between the two Númenórean armies, and almost captured. Though he escaped in the end and returned to Mordor, he swore vengeance on the victorious Númenóreans. More than 1,600 years later, he accomplished his aim and Númenor was destroyed, so that Ciryatur's great victory can be seen as the first seed of the Downfall of his homeland.