Ten thousand ships
Around 700 years before Aegon's Landing, the expansion of the Valyrian Freehold into the western coastal regions of the eastern continent threatened the great city-states of the Rhoyne, a vast river network of the east. The ruler of one of them, the warrior queen Nymeria, managed to unite the Rhoyna and they began an evacuation to Westeros, allegedly fleeing in ten thousand ships across the Narrow Sea. The fears of the Rhoynar were proven when the Valyrians destroyed the city of Arnar which tried to resist them. Nymeria's host landed on the eastern coast of Dorne. Nymeria made common cause with Mors Martell, a local lord who was one of dozens if not hundreds of powerful lords controlling the patchwork of states in Dorne. With Nymeria's vast host at his command, Mors was able to unite the entire peninsular of Dorne under his rule. No less than seven self-styled rival Dornish kings were captured and sent to the Wall in golden fetters. In the Rhoynar style he took the title "Prince" and introduced primogeniture. The fortress of Sunspear was made capital of Dorne, and House Martell has ruled ever since.