The Siege of Castle Cousland, also known as the Battle of Highever, was fought in 9:30 Dragon between the Teyrnir of Highever and the Arling of Amaranthine. Under the command of Arl Howe, Amaranthine's forces occupied Highever itself and laid siege to Castle Cousland, overtaking it within hours. The conflict was a result of treachery by Arl Howe against Teyrn Cousland, resulting in the near-annihilation of the Cousland family line and the conquest of Highever by Arl Howe, who later became Teyrn of the land under the de facto rule of Regent Mac Tir. Though fought shortly before the beginning of the Fereldan Civil War, it was later a major factor in the discord among the Fereldan nobility, not least because of Mac Tir's support of Howe and his actions.
Highever was one of only two teyrnirs, the other being Gwaren, granting the Cousland family power and influence second only to the King. Teyrn Bryce Cousland, ruler of Highever and the patriarch of the Cousland family, became a very powerful, influential, and popular noble, with some even suggesting he take the throne of Ferelden rather than King Cailan.
Despite initially opposing the Howe family during the Orlesian Occupation, the Couslands and Howes became close friends afterward, with Teyrn Cousland and Arl Howe, ruler of Amaranthine, fighting in battle together and sharing a close camaraderie. Despite this, however, Arl Howe grew increasingly irritated by Bryce's support of King Cailan, whom he greatly disliked. He also harbored deepening jealousy of Bryce's influence and power, resenting that his family, whom he deemed "nobler", was of lower social and political statue than the Couslands. It is unknown when he planned his treachery, though it is known when he enacted it.
In 9:30 Dragon, as the Fifth Blight approached, King Cailan ordered all available forces in Ferelden to muster at the fortress-ruin of Ostagar. Howe arrived at Castle Cousland and claimed his forces were delayed by poor weather, which resulted in Teyrn Cousland dispatching his own forces, led by his son Fergus Cousland, to Ostagar ahead of him, leaving Highever almost entirely unguarded. However, the delay was intentional, and in reality Howe was planning a clandestine takeover of Highever and the destruction of the Cousland family line.
During the night, after Highever's forces departed for Ostagar, Arl Howe's troops swiftly attacked, occupying Highever's lands and laying siege to Castle Cousland. Whether by treachery or sabotage, Howe's forces made their way into the Castle within moments of arriving, overrunning the handful of guards left there. Rather than take prisoners, Howe's forces began systematically slaughtering everyone they came across, including innocent noncombatants.
Under the command of Ser Gilmore, the remaining guards in the Castle attempted to hold off Howe's advance, but ultimately failed. Howe's forces breached the castle's front gates and overwhelmed him. As Howe's forces swarmed over the Castle, every last soldier of Highever fell, and ultimately both the Teyrn and Teyrna were slain by Howe's forces. In a matter of hours, Castle Cousland, and indeed all of Highever, was in Amaranthine's control.
Any soldiers left in Highever were killed or captured, and every living person within Castle Cousland that could not escape was slain, including Fergus' wife and son, Oriana and Oren. Castle Cousland was occupied by Howe's troops, and despite being heavily damaged in the fighting, he made little effort to repair it.
Believing he had wiped out the Couslands, Howe assumed control over Highever. King Cailan was furious at his treachery, and had the Battle of Ostagar gone well, he planned to send his armies northward to reclaim Castle Cousland and ensure Howe's execution. However, with Cailan slain at Ostagar and Loghain Mac Tir taking his place as Regent of Ferelden, he instead had formed a close alliance with Rendon Howe, making him Teyrn of Highever and Arl of Denerim. The conquest of Highever was one of several sparks in the fire of the Fereldan Civil War, and Mac Tir's support of Howe could not be easily explained off.
After the Fifth Blight ended, Fergus Cousland was elevated to Teyrn of Highever and reclaimed his family's lands, as well as Castle Cousland, which had fallen into disrepair under Howe's intentional negligence. Fergus rebuilt the Castle and Highever itself, with the Teyrnir once again raising to great prominence several years later.
- In the Human Noble Origin, Highever remains on the world map after departing it, but it cannot be traveled to.
- If the Human Noble Origin is chosen, the battle goes somewhat differently, with the future Hero of Ferelden and the veteran Warden-Commander Duncan fighting their way out of the Castle, escaping, and warning Fergus of Howe's treachery. Fergus still takes up the role of Teyrn, however, with his brother or sister remaining a Grey Warden or Fereldan royalty in the end.
- If any other Origin is chosen, the battle still occurs, though it is only mentioned and never witnessed directly.