Siege of Barad-dûr
The Siege of Barad-dûr was the last battle of the War of the Last Alliance and the Second Age, following on after the Battle of Dagorlad.
The Last Alliance of Elves and Men gathered in Mordor and surrounded the Dark Lord's stronghold. Gil-galad, Elendil and Thranduil laid siege to the tower, but could not breach its gates.
Sauron fought back with projectiles thrown from his walls, and in this manner killed King Anárion with a thrown rock. Eventually however, Sauron himself rode forth and met his enemy on Mount Doom. There, he struck down both Gil-galad and Elendil and broke the Númenórean King's sword Narsil. Elendil's son Isildur took up the broken sword however, and cut the One Ring from Sauron's hand. Thus, Sauron was defeated and his army laid low. Círdan and Elrond bade Isildur cast the ring into the fires of Mount Doom, but this he refused, and brought the ring with him out of Mordor.