Harrenhal is an enormous ruined castle and is the site of many important events in the novels. Harrenhal was built by Harren the Black, after his conquest of the Riverlands, intending to make it the largest fortification ever built in Westeros. The castle has been described as so large that an entire army was needed to garrison it. The Great Hall had 35 hearths and seated thousands. Shortly after the castle was completed, Aegon the Conqueror's dragon slew Harren, his sons, and his entire army by setting the castle alight.