Catelyn Stark: On the shores of the Gods Eye due north of the Isle of Faces rises a monument of arrogance and cruelty: Harrenhal. For a people who prided themselves on their ships, the Ironmen of old seized any chance to leave them, and carve out a vast kingdom from the peaceful Riverlords. Their empire reached its zenith under King Harren Hoare, called "the Black" by those he terrorized; and his own men, though they meant it proudly.
King Harren enslaved the Riverlands to raise the mightiest fortress Westeros had ever seen; a castle that could garrison a million men, with walls so vast that winters would come and go and besieging armies grow old and grey before the castle fell. Five towers he ordered, reaching into the heavens like grasping fingers; a monstrosity which he forced our the people to build for their own subjugation.
But the day the slaves laid down the last stone, Aegon Targaryen and his sisters arrived in the south. When they arrived with their small army, Harren laughed and shut the gates. Harrenhal was given an easy first test, and an easy one at that.
It failed. Harrenhal could have survived all the armies of Westeros combined, but Harren learned that the tallest and thickest walls meant little to dragons; for dragons fly. With Harren and his sons dead, Harrenhal quickly surrendered to Aegon. House Tully then raised the Riverlords in rebellion against the Iron Islands, and with Aegon we flushed the ironborn to the sea. We should've torn down the castle stone by stone then;, but Harrenhal seemed such a magnificent prize Aegon gave it to one of his commanders, whose line then withered to extinction; as would every family to hold it thereafter.
When many speak of Harrenhal, their voices drop to whispers. About Mad Lady Lothston, who was said to send a giant bat to send children for her crock pots, and to bathe in blood and serve feasts of human flesh. About the ghosts of Black Harren and his sons who still walk the castle at night, all aflame. Of the servants who went to bed in full health and were found in the morning burnt to ash.
Mere stories to frighten wayward children and excite young girls you may say? You would not be entirely wrong. Harrenhal is a prize; a nigh impregnable castle with enough land and income to make a man, at a stroke, one of the greatest lords in Westeros. But you would not be entirely right, either. Say by a king's grace Harrenhal became yours, now you must garrison it, you must repair it and maintain it. Even stretched to the end of your means you cannot not fill and manage the whole castle. So you would retreat your household to four of the five towers. Then three, then two, then only the bottom thirds of those. You close the Hall of the Hundred Hearths and take your meals in your rooms. Even then you can't shake the feeling of desolation; that Harrenhal and it's vastness is devouring you. In later years, as you bury a grandson or a great-grandson - the last of you line - you will know it has.
During the brief montage when Catelyn explains that every House which ever held Harrenhal was struck by tragedy and went extinct, a montage shows a series of Heraldry banners burning away to signify the death of each of these Houses. While the names aren't mentioned on-screen, these heraldry designs accurately correspond to the Houses which held Harrenhal in the books, and even progress through the montage in chronological order: House Qoherys, House Towers, House Harroway, House Strong, and House Lothston.
The castle itself is held by House Whent at the beginning of the TV series, but the last living member was old Lady Shella Whent, whose children had all died. Shella herself died (apparently due to old age and stress) after the Lannisters invaded Harrenhal in Season 2 (though this was off-screen and not directly stated).
House Whent apparently only went extinct in the male line, however, as Minisa Tully (Catelyn's mother) was herself born a Whent, and thus Catelyn, Lysa, Edmure, and all of their respective children would technically have some claim to Harrenhal. However, because the Lannisters consider the Tullys and the Starks (Catelyn Tully's children) to be in rebellion against the crown, they opt to simply award the castle to Petyr "Littlefinger" Baelish - who then marries Lysa.
- King Harren Hoare, the "Black" (mentioned)
- King Aegon I Targaryen, the "Conquerer"
- Queen Visenya Targaryen (mentioned)
- Queen Rhaenys Targaryen (mentioned)
- Balerion, the "Black Dread" (not mentioned by name)
- Vhagar (indirectly mentioned)
- Meraxes (indirectly mentioned)
- Mad Lady Danelle Lothston
- Lady Shella Whent
Heraldry seen in passing during a montage: