Riverrun is a strong three-sided castle, although not especially large, situated at the point where the Tumblestone and Red Fork rivers meet. A moat on the third side of the castle can be flooded to leave it practically unassailable. The Tullys were never kings but were the chief leaders of the rebel riverlords who deserted Harren the Black and joined Aegon the Conqueror and so were rewarded with overlordship of the lands watered by the Trident. Their motto is, “Family, Duty, Honor.”
Lord Hoster is an old man, afflicited with an illness which has left him a bed-ridden invalid. His son and heir is Ser Edmure, a proud, hot-tempered, short-sighted man. Lord Tully joined the rebellion against Aerys, in part because Brandon Stark and his lord father Rickard had arranged a marriage with Lord Tully’s eldest daughter Catelyn before their deaths. Eddard Stark fulfilled the marriage contract and Lord Tully’s younger daughter Lysa was wed to Lord Jon Arryn.
Information about House Tully that reveals spoilers from the books.