Ilinalta's Deep

Initially an Imperial fort, Ilinalta was destroyed by an unknown disaster several decades before the civil war erupted in Skyrim. Neither the Imperials nor the Stormcloaks made any attempt to salvage the ruin. The ruin became inhabited by several necromancers, who used it as their base of operation for several years.

By 4E 209, the fort was taken by vampires from the Bloodlet throne coven. Reconstruction on the ruin was started, and finished by the end of the year. It was transformed into a prison-fortress, used to contain the prisoners of the Bloodlet throne coven. It also served as the base for the Inquistorius Vampirum.

History
Ilinalta's Deep was originally fort Ilinalta, built and garrisoned by the Empire, late in the third era. It served as an Imperial base in the region, and due to its proximity to lake Ilinalta, was fairly self sufficient. In the early years of the fourth era, the fort fell victim to a natural disaster, and most of it was destroyed, collapsing into fort Ilinalta. For years afterwards, locals went out of their way to avoid it, believing it, and the area, cursed.

The Empire made no attempt to rebuild the fort, with the surviving Imperials marching to fort Neugrad, located in eastern Falkreath hold. Neugrad remained the Imperial base of operations in the area up to and for the duration of the civil war in Skyrim.

On the 17th of Last Seed, 4E 180, a group of necromancers took up residence in the ruin. Using the reanimated remains of Imperial soldiers, they managed to rebuild the fort to some degree. However, a series of battles that took place there lead to the ruin being abandoned in 4E 184.

The ruin remained abandoned for the next two decades, due to its' reputation of being haunted, and the lack of tactical advantage it offered the current Imperial troops in Skyrim. It was overlooked during the civil war, as both the Stormcloaks and the Imperials lacked the manpower and resources to rebuild it.

The ruin was scouted by members of the Bloodlet throne coven, during the Blight war, in the closing days of 4E 208. As the coven was in need of further outposts, in order to fortify their hold on Falkreath hold, the decision was made to rebuild the fort. Duros Kaast was selected to oversee the construction of the fort. However, shortly after construction was started, the war ended, on the 3rd of Morning Star, 4E 209.

Despite this, the reconstruction continued. At Kaasts' suggestion, the fort was changed into a prison fortress, and the base of the Inquisitoris Vampirum. He was placed in charge and the inquisitors moves from the Bloodlet throne to Ilinalta's Deep. The fortress used the surrounding landscape to its' advantage, with lake Ilinalta to its' back. A high tower was built in the center of the fortress, from which someone could survey the surrounding land.

The prison held captives of the coven, such as surviving members of the Dawnguard, and members of the Order of the Silver Sun .Those that were believed to have information were tortured for information. Ilinalta's Deep gained a dread reputation, and much of the surrounding lands became abandoned, save for the inquisitors. When the cult of Molag Bal and its' allies came into power halfway through 4E 210, they besieged the prison fortress, though the besiegers were eventually defeated.

Quentil Meer was held prisoner there for several months, before the Order of the Silver Sun launched an assault to rescue him.