Andal Invasion Edit
House Martell was founded by Morgan Martell, an Andal adventurer who settled between the mouth of the Greenblood and the Broken Arm. Morgan led the defeat of the local First Men, including Houses Wade and Shell, and the Martells ruled a strip of land fifty leagues long and ten leagues wide. They did not rule as kings, but were cautious vassals of kings from Houses Jordayne, Allyrion, and Yronwood, as well as petty kings of the Greenblood.
Nymeria's War Edit
At the time of the Rhoynish Wars, the Martells were one of the lesser ruling families of Dorne, which was a collection of feuding petty kings and lords even as the other regions of Westeros began to consolidate into larger realms. When Nymeria, the warrior queen of the Rhoynar, came with her people to Westeros from Essos in ten thousand ships, the Martell lands were dwarfed by those of House Yronwood. However, Nymeria took Mors Martell, Lord of the Sandship, as her husband and, combining their strength, the two managed to unite all of Dorne under their rule in Nymeria's War; House Nymeros Martell has reigned since.
The union of their peoples saw the Martells abandon many of their older Andal customs in favor of those of the Rhoynar. Nymeria named Mors Prince of Dorne instead of king, and their lands and title passed down to their eldest child, their daughter, regardless of Nymeria marrying again after Mors's death and giving birth to a male child. The Spear Tower and the Tower of the Sun, the towers of Sunspear's Old Palace, were built in the Rhoynish fashion.
Targaryen Wars Edit
After Aegon I Targaryen waged his War of Conquest, he came to Dorne. In the First Dornish War his army was bled dry by guerrilla warfare in the desert, a situation in which his dragons were of little use. Deciding that conquering Dorne would be too costly, the Conqueror opted to leave the Martells as sovereign princes. House Martell kept Dorne independent from the Targaryens for two centuries, the only one of the Seven Kingdoms to manage such a feat.
In 110 AC the Martells joined the Triarchy in the war against Prince Daemon Targaryen in the Stepstones. Daemon's brother, King Viserys I Targaryen, spoke of wedding his daughter Rhaenyra to the Prince of Dorne as a way of finally uniting the Seven Kingdoms, though ultimately this did not occur.