Battle of the Gwathló
Siege of Eregion - First Siege of Imladris - Battle of the Gwathló
The Battle of the Gwathló was the decisive battle of the War of the Elves and Sauron that brought an end to Sauron's power for many centuries. The Battle of the Gwathló is regarded as the second biggest battle in the history of Middle-earth, only surpassed by the War of Wrath.
History
After being driven back from the Grey Havens and after heavy losses at Sarn Ford, Sauron's forces regrouped and joined with his forces in Tharbad where they were assailed by the pursuing forces of Gil-galad and Númenor and then by another force of Númenóreans sailing up the Gwathló and attacking from their rear.
In the battle Sauron and his armies were utterly routed. The remaining survivors narrowly escaped but were assailed again by the Númenóreans in the east of Calenardhon and destroyed, leaving Sauron with little more than a bodyguard to escape back into Mordor.
The ensuing victory left Sauron's power crippled but not destroyed, and he slowly rebuilt his strength over a thousand years until the thirty-third century, when he challenged Ar-Pharazôn for dominance of Middle-earth.
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References
Location: Grey Havens