House Allyrion of Godsgrace holds their seat at the confluence of the Scourge and the Vaith where both rivers empty into the Greenblood, commanding one of the great river crossings of eastern Dorne. Their words, No Foe May Pass, speak plainly to the purpose of that posting. The house is old enough that the early Martells owed them fealty rather than the other way around; only after Princess Nymeria led her ten thousand ships to the shores of Dorne and made common cause with the Martells did the hierarchy of the Dornish lords settle into its present order, with Allyrion yielding pride of place to Sunspear.
By the time of A Game of Thrones the seat is held by Lady Delonne Allyrion. Her son and heir, Ser Ryon Allyrion, is wed to Ynys of House Yronwood, and Ryon has at least one bastard son, Daemon Sand, called the Bastard of Godsgrace. Godsgrace and its garrison remain a reliable sword for the Martells, and the house's ancient words are taken no less seriously for the centuries that have passed since they were first cut into stone.