The Stepstones are a series of islands running from the Broken Arm of Dorne to the Disputed Lands of Essos, effectively separating the Narrow Sea from the Summer Sea. There are a number of large islands and several smaller ones, along with many hazardous reefs and small rocks in the area.
According to legend, the Broken Arm used to be a land-bridge linking Westeros to Essos, and across which the First Men migrated. The Children of the Forest are reported to have destroyed the Arm with magic to prevent the First Men's movements, but by the time this had happened, the humans' numbers had become too great. A further attempt to shatter the Westerosi continent in two by destroying the narrowest point of land at the Neck failed, merely resulting in the creation of vast marshlands and flooded regions.
In more recent times, the Stepstones have become one of the many battlegrounds between the Free Cities of Lys and Myr, who war over them and the nearby Disputed Lands, sometimes involving Volantis as well. Roughly fifty years ago it was the site of the War of the Ninepenny Kings, when nine noble lords of disparate origin joined forces to help one another seize their objectives which they could not hope to achieve by themselves. Maelys Blackfyre, known as Maelys the Monstrous, planned to use the Stepstones as a base to invade Westeros and seize the Iron Throne in the name of his ancestor, Daemon. However, King Aegon V Targaryen learned of this threat and despatched a fleet and an army to stop Maelys' plans. The Westerosi armies were successful and Maelys was killed in battle by Ser Barristan Selmy.
The Stepstones are today a morass of petty independent kingdoms and pirate havens. Attempts by both the Seven Kingdoms and the Free Cities to conquer or subdue the islands have failed due to the difficulty of holding territory and keeping open supply lines through the pirate-infested waters.