From A Wiki of Ice and Fire
Dorne is large peninsula which makes up the southern-most part of Westeros, and is one constituent regions of the Seven Kingdoms. Its capital is Sunspear and the lords of the ruling House Martell still style themselves "Prince" and "Princess" in the Rhoynish fashion.
Dorne is bordered by the Sea of Dorne to the north, the islands known as the Stepstones to the east, and the Summer Sea to the south. Stretched between them is the mountain range known as the Red Mountains, which separates Dorne from the remainder of the Seven Kingdoms by land. There are only two major passes though the Red Mountains, connecting Dorne with the rest of the continent by land, the Stone Way Pass and the Prince's Pass. The Prince’s Pass leads to the Reach, while the Boneway exits the mountains near Summerhall.
Dorne is the hottest region on Westeros. The region is rocky, mountainous, arid and dry, and features the only desert on the continent. Its rivers provide some fertile lands and even during a long summer there is enough rain and other supplies of water to keep Dorne habitable  Inland water is almost as valuable as gold, and wells are jealously guarded.
- Sunspear, the seat of House Martell, the ruling family of the region.
- Starfall, the seat of House Dayne.
- Yronwood, the seat of House Yronwood, the most powerful of the Martell bannermen.
- Planky Town, a trade port town at the mouth of the Greenblood.
- Main article: Dornishmen
Dorne is the least populous of the Seven Kingdoms . Dornishmen differ both culturally and ethnically from other Westerosi due to the historical mass immigration of Rhoynish people and their relative isolation. Dornishmen have adopted many Rhoynish customs on top of their Andal origins. Dornishmen have a reputation for hot-bloodedness and sexual licentiousness, and are still viewed with some mistrust and rivalry by the people of the Dornish Marches. Dornish bastards are given the surname Sand.
Dorne provides many exotic products which are uncommon in the rest of the Seven Kingdoms, in particular, citrus fruits and Dorne's own special wines. Lemons, olives, and pomegranates come chiefly from Dorne. Many of these plants are grown with the aid of canals that bring water from streams and rivers. Dorne is also famous for the sand steed, a type of slim but swift horse bred in only in Dorne, which can run for near two days before tiring.
Ships from the Free Cities such as Volantis trade at the port town Planky Town, which is located at the mouth of the river Greenblood, allowing transport of goods across the land. Caravans take on supplies at Sunspear before crossing the deep sands to reach the Prince's Pass.
The First Men settled Westeros by crossing the land bridge across the Narrow Sea called the Arm of Dorne. During their great war with the First Men, the Children of the Forest broke the Arm in an attempt to stop them coming.
One thousand years ago, Dorne was a coalition of Andal states and petty kingdoms, with no ruler strong enough to seize control of the entire region, until the Rhoynar Invasion which forced the people of the Rhoynar to flee, led by their legendary warrior-queen Nymeria, they left in a fleet of 10,000 ships, arriving to Dorne. Nymeria made alliance with Lord Mors Martell of Sunspear, and with his support conquered the entire peninsula, uniting it as the Kingdom of Dorne with House Martell as its ruler. The Rhoynar brought their own gods with them to Dorne, but they have largely disappeared in favor of the Faith. Nevertheless, many Rhoynish customs, including inheritance regardless of gender, have been absorbed into Dornish society.
Dorne has had a violent history, particularly with the mountain houses, who lived by raiding across the borders into the marches, feuding with each other endlessly. Dorne and the Reach fought border wars beyond count and made countless raids across mountains and marches even when at peace, leading to their great enmity.
Seven centuries after the Andal invasion, Aegon the Conqueror invaded Westeros and in his War of Conquest subjugated all of the Andal kings one by one, except Dorne, which successfully resisted the Dragon King. Whereas other kings and lords had taken to the field against Aegon, or clustered in castles, the Dornish refused to give open battle and allow Aegon to deploy his dragons. Instead, they turned to ambush and raids, striking quickly and then slipping back into the desert or through the mountain passes, where even the dragons could not find them. In time, Aegon pulled away from Dorne.
A century and a half later King Daeron I, the Young Dragon, managed to do what his ancestor could not and successfully subdued the kingdom. Unfortunately, it almost immediately rose in rebellion. In the resulting conflict, forty thousand soldiers gave their lives, forcing the Targaryens to pull away from Dorne. After Daeron's death, his brother and successor Baelor the Blessed made peace with Dorne instead, marrying off his cousin, another Daeron, to Myriah Martell. When this prince ruled as Daeron II, he made another marriage pact, offering his younger sister Daenerys to the ruling Prince of Dorne Maron Martell, finally joining Dorne to the rest of the Seven Kingdoms through a peaceful alliance. Before officially joining the realm, the Dornishmen fought alongside Daeron II's forces (being led by his half-Martell son Baelor Breakspear), helping to suppress the Blackfyre Rebellion.