House Brax of Hornvale is reckoned among the chief bannermen of Casterly Rock, and one of the older noble lines of the westerlands. Their seat lies east of the Rock in the green country beyond the Golden Tooth, where the Brax lords have long answered the lions' summons with horse and lance and a sigil all their own: a purple unicorn upon a silver field, fancier than most westermen will admit to envying.
At the opening of A Game of Thrones Lord Andros Brax keeps Hornvale and his sons keep the field; when Lord Tywin Lannister rides east to chastise the Tullys, Brax horse rides with the lion banners. Lord Andros will not see the war's end — drowned in the rout at the Camps when Robb Stark's wolves break the western host — and his son Ser Tytos will come into Hornvale with the war still half-fought. The unicorn rides on under both lords.