The Battlespire, also known as the Spire and Celestial Citadel, was the magical war academy of the Imperial Battlemages, and a testing facility for candidates seeking to join the Imperial Guard. It was (and its ruins remain) located in a Slipstream Realm deep in Aetherius according to some sources, while others place it in the vast emptiness of Oblivion As the mortal mind can be driven to madness by Oblivion, these sorts of realms are useful as they allow the mind to acclimate to the contradictory nature of the outer realms without the same levels of mental strain. More simply, it was possible to access numerous realms of Oblivion from the Spire through the use of teleportals and voidgates. The facility was moored in place by five great Anchors, which assured its safety and stability in the surrounding flux. Access to the edifice was granted via the Pillar of Light, a teleportation device linked to the Weir Gate.
Though the date of the construction of the Battlespire Academy remains obscure, both the academy and the Weir Gate were known to exist as of 2E 582. The institution was accepting recruits by the time of the Three Banners War in 2E 580.
After numerous failed attempts in the past, the Daedric Prince Mehrunes Dagon succeeded in capturing the Battlespire during the Imperial Simulacrum. Dagon had been instrumental in Jagar Tharn's imposture and assumption of the Imperial throne. In return for his assistance, Tharn gave the Battlespire to the Prince, on the condition that Dagon eliminate Tharn's rival battlemages within. In 3E 398, Mehrunes Dagon collected his prize. The Prince's forces, led by Imago Storm of Clan Dremora, mustered in the Havoc Wellhead, then rampaged through two other planes of Oblivion—the Shade Perilous of Nocturnal and the Soul Cairn—before invading the Battlespire itself.
Shade Perilous was home to two Daedra clans, the lordless Seducers and the Nocturnals who had given them refuge. The Nocturnals were imprisoned in their own demense as the Seducers were bent to Dagon's will. However, some Seducers willingly entered his service, and these converts were remade in the image of Dagon's greed and treachery, making them much more powerful—and giving them wings. These "Dark Seducers" joined the ranks of the invasion forces, with some being given Daedric Crescents to wield in battle. One Dark Seducer in particular became Mehrunes Dagon's bodyguard and lover, and was entrusted by the Prince with one of his artifacts, the Sword of the Moon Reiver. Once the Battlespire was taken, the Weir Gate, the portal to Tamriel, was sealed with Dagon's personal warding sigil.
Unaware of these events, a pair of apprentice battlemages, Shadow Legion aspirants, entered the Battlespire after it had fallen. One apprentice went ahead, leaving behind notes and helpful items, but was ultimately captured by the Daedra and brought to Dagon's hunting lodge before the Prince himself. The other apprentice went in search of the first (and for a way back to Tamriel) by fighting through, bluffing past, and making deals with the various forces, Daedric and otherwise, along the way.
After following the trail back to the Shade Perilous, the apprentice befriended the Nocturnals and freed their leader, Jaciel Morgen. Curiously, Clan Dremora also offered its assistance, for while Mehrunes Dagon had allowed his armies to enter Shade Perilous and use it as a waystation for the assault on the Battlespire, he had not sanctioned its overthrow or occupation. Instead of negotiating for passage or showing restraint, Dagon's protégés and adoptive children, Faydra Shardai of the Fire Daedra clan and Xivilai Moath of the Frost Daedra clan, decided to crush their long-time enemies, the Nocturnals. The Dremora believed this needed to be undone in order to rectify things.
However, the path from the Shade Perilous led to the Chimera of Desolation, where the apprentice became the hare in a Great Hunt. While the Dremora could offer little help there, the apprentice was able to survive and locate Chimere Graegyn. Chimere drew on his past experience with Mehrunes Dagon to help the apprentice escape the realm, offering up the Savior's Hide, as well as knowledge of the Spear of Bitter Mercy to end the hunt. The most vital information he provided was Dagon's protonymic, which can be used to banish him. However, it is likely that by this time, the Prince had added an unknown neonymic as well.
Once through the Chimera, the apprentice wound up in the Havoc Wellhead, and came face to face with Grand Vizier Imago Storm of the Dremora. Storm was of the opinion that with the conquest of the Shade Perilous combined with the taking of the Battlespire, Clan Dagon had "overreached its resources and  Storm then gave the neonymics of all three to the apprentice, as the mortal had little choice but to go along with this plan.". He felt it best if Faydra, Xivilai, and Mehrunes Dagon himself were temporarily removed from the picture so he could restore order and stability to Clan Dagon.
After dealing with the lesser Daedra, the apprentice portaled into the Deadlands near Dagon's hunting lodge, the Prince's personal pleasure palace. According to the Dremora, banishing Mehrunes Dagon required the Armor of the Savior's Hide, his proto- and neonymics, the "aid of absent friends", a bit of hope, and a weapon made from Dagon's own substance, the Sword of the Moon Reiver. This last item was soon taken by force from Dagon's Dark Seducer lover, and the apprentices battled up a mountainside and entered the lodge to face Dagon himself.
Mehrunes Dagon was waiting in his inner sanctum with the first aspirant, who was chained from the ceiling and paralyzed. The Lord of Destruction smugly thanked the mortal for bringing him so many valuable magic items, though he was perturbed that the Savior's Hide prevented the paralytic effect. And more so when the apprentice revealed knowledge of Dagon's nymics. But the Prince remained smug until the apprentice revealed the Moon Reiver, at which point he decided to take action. But in that moment, the apprentice summoned Jaciel to the battle; her sudden appearance momentarily distracted Dagon, giving the apprentice enough time to strike. Dagon was sucked back into the Void, being "compressed into an ever-smaller volume" before vanishing.
The Battlespire was partly destroyed during the invasion's aftermath. The Empire reclaimed the ruins, and gathered up all the Daedric Crescents to be destroyed, bar one. These events led to the conclusion that investment into its reconstruction was both unfeasible and undesirable at the time, due to the installation being a great temptation for Daedra to target. Therefore, discussions were brought up to leave the gates to the Spire sealed indefinitely.
- Clarentavious Valisious, Venerable Artificer
- Samar Starlover, Armsmaster, Master of the Serpent Blade and a Dragoon (Elite Imperial Dragon mount guard)[UOL 1]
- Grad Helthen, Spellmaster and Grand Ipsissimus of the dissolving fires.
- Paxti Bittor, Exalted Summoner and Lion-Lord Invoker Pursuivant.
- Mactana Greenway, Gatekeeper
Recruits of the Battlespire are known as Potentials and are usually identified as such around the age of 12. These Potentials learn magic, magical and martial warfare, and contemporary studies. Every year there is a Potentials Battle Tourney, where single combat is known to be a part of it.
The Emperor also has a personal liaison to the Battlespire, with the title of this position being the Imperial Secretary. Lomegan Marie held this position circa 3E 398.
Some of the Battlemages, including the ones above known to have been at the Battlespire during its invasion, are:
- Arcem Terastang
- Kirel Aman, Praeceptor Superior
- Tuscan Daphsir
- Tutawan Soal
The Battlespire consists of many notable locations, with a lot of these relating to the daily function of the college, for example, the High Court Room. The Battlespire also contained a large room for dragons such as Dragonne Papré.
The Star Galley Crib
Aside from the Weir Gate itself, the only access to the colleges was via the Star Galley, a magic boat which could navigate the surrounding environs. The vessel was constructed by Battlemage and Artificer Clarentavious Valisious, and was kept in the Star Galley Crib near the Weir Gate, though access was normally restricted.
This section of the facility is also notable for being the home of the gigantic Mock Turtle.
The High Halls and Librarium
The upper sections of the Battlespire consist of the war college itself. Here are found dormitories, mess halls, libraries, lecture halls, an infirmary. Other areas found here are the Great Hall, the Conjury Hall and the Summoning Hall.
Of particular importance was the voidgate. This device, powered by artifacts known as voidguides, allowed passage to Oblivion. The Soul Cairn was accessed in this manner during Mehrunes Dagon's invasion, but it is not known which other realms the voidgate was able to reach.
Several realms of Oblivion were known to be accessible from the Battlespire or from each other. These include the Soul Cairn, Shade Perilous, the Chimera of Desolation, the Havoc Wellhead, and Dagon's Hunting Lodge in the Deadlands.
- According to The Doors of Oblivion, years after Dagon's invasion was defeated, the mage Morian Zenas and his apprentice attempted to use the remains of the Battlespire to enter Oblivion. They found that although the Weir Gate still stood and the shattered academy remained accessible from Mundus, the link to Oblivion had been broken. However, this is contradicted by the Crafting Motifs series, according to which the two lived in the Second Era. Copies of The Doors of Oblivion were also available at this time, but no mention of the Battlespire was seen within.
- Letter to the Grand Marshall of the Imperial Legion by Clarentavious Valisious
- Meet the Character - Lucilla Caprenia by Martus Tullius — A request for deployment of an apprentice Imperial Battlemage
- Starlover's Log by Samar Starlover — Entries from the journal of a Battlemage seeking escape from Battlespire
- Ideal Master dialogue in Battlespire
- Events of Battlespire
- The Doors of Oblivion — Seif-ij Hidja
- Battlespire Athenaeum — Ronald Wartow — Ronald Wartow
- Elderscrolls.com Codex Archive
- ESO Loremaster's Archive — Lord Fa-Nuit-Hen and Tutor Riparius Answer Your Questions
- Great Anchor warning plaque in Battlespire
- Battlespire opening cinematic
- Scute of the Mock Turtle item description
- Starlover's Log — Samar Starlover
- Sirran Angada's dialogue in Battlespire
- Elderscrolls.com Archive Timeline
- Letters for the Battlespire Hero — Vatasha Trenelle or Josian Kaid
- Frost Daedra's dialogue in Battlespire
- Ideal Master's dialogue in Battlespire
- Deyanira Katrece's dialogue in Battlespire
- The Dark Seducers' appearance in Battlespire
- Letters from the Dremora
- Dark Seducer Bodyguard's dialogue in Battlespire
- Letter to Mactana
- Imago Storm's dialogue in Battlespire
- Dremora Informant's dialogue in Battlespire
- Events of the Shade Perilous in Battlespire
- Dremora Oathkin's dialogue in Battlespire
- Events of the Chimera of Desolation in Battlespire
- Old Man Chimere's dialogue in Battlespire
- Events of the Havok Wellhead in Battlespire
- Imago's Notes about Neonymics — Imago Storm
- Events of Dagon's Hunting Lodge in Battlespire
- From private correspondence of Julianos Cennan, Chamberlain to Uriel Septim
- Tamrielic Lore — Yagrum Bagarn
- Elderscrolls.com Timeline
- Meet the Character - Lucilla Caprenia — Martus Tullius
- Jagar Tharn's Letter — Jagar Tharn
- Scamp's dialogue in Battlespire
- Letter to the Grand Marshall of the Imperial Legion — Clarentavious Valisious
- Star Galley Crib Note
Note: The following references are deemed to be unofficial sources. They are referenced to provide a rounder background to this article and may not consist of definitive lore.