Cair Andros, meaning "Ship of the Long-Foam," was an island in the river Anduin, resting nearly forty miles to the north of Osgiliath. It was of paramount importance to Gondor during the long war with Mordor in order to prevent the enemy from crossing the river and entering into Anórien.
The namesake of this island was derived from the long shape of the isle, which was boat-like in nature, and the effects of the water breaking upon what was seen as the prow of the ship. The island was around ten miles in length, and narrowed toward its northern end, creating the prow. Cair Andros was one of the main sites used to cross the river Anduin, along with Osgiliath to the south. As the northern parts of the river were nearly impassable marshland, and the south of the river near Lebennin became too wide to ford safely, these two locations were critical to both Gondor and Mordor during the war.
Cair Andros had a steady garrison, and was well-maintained until the outbreak of the War of the Ring; military incursions were expected both here and at Osgiliath, but the southern crossing was considered by Denethor II to be of more importance, and therefore was more heavily guarded. Being a vital point in Gondorian defenses, a crucial river junction, and due to the fact that it was less manned than was Osgiliath, shortly before the Battle of the Pelennor Fields, Sauron sent a force of orcs and Easterlings from the Morannon to lay siege to the fort, and the island was overrun in the Battle of Cair Andros. Around the time of the fall of Osgiliath, fugitives began arriving at Minas Tirith from Cair Andros.
Aragorn, during his march toward the Black Gate, sent soldiers to reclaim the island for Gondor; these soldiers were young men of Rohan and Lossarnach, and were eventually successful in their quest to retake the island. After the fall of Sauron and the conclusion of the war, the island continued to serve as a vital place of crossing, and the Captains of the West set sail from Cair Andros on their way down the Anduin to Osgiliath.
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