A boat-shaped island in the Anduin just south of the Nindalf, Cair Andros ("Ship of Long Foam") is named for the way the river foams as it strikes the rocks of the island's high, prow-shaped, upstream end.

Situated at the first crossing point of the Anduin south of Emyn Muil, Cair Andros served as a major defense against enemies crossing the Anduin to do battle against the forces of Gondor and Rohan throughout most of the Third Age.

It is not known when the island was first fortified but it is written that during the reign of Turin II, the 23rd ruling Steward of Gondor (2914-2953) and great-grandfather of Denethor II, the fortifications were rebuiltand improved.

On March 10, 3019 the island fell to the forces of Sauron and was used a a crossing point to Anorien. It was these forces that stood between the Riders of Rohan and Minas Tirith at the Battle of Pelennor Fields.

On March 23rd, during the march to the Black Gate of Mordor, King Elessar sent a small part of his force (those too scared to continue into Mordor) to retake Cair Andros. It is not stated whether the Island was abandoned or they had to fight to reclaim it.

Towards the end of May of that same year Frodo sailed from Cair Andros to Osgiliath, on his route to Minas Tirith after the destruction of the Ring.
Encyclopedia entry originally written by PotbellyHairyfoot