The Twins is a large double castle straddling the Green Fork river; the two halves of the castle are connected by a bridge that is the only crossing of the river for hundreds of miles. The Twins is the seat of House Frey, which has grown wealthy by charging a toll of all those who cross for the past six centuries. Because the Freys are both wealthy and numerous, theirs is one of the most powerful houses sworn to House Tully. The castle's strategic position gives House Frey enormous importance in times of war.