The Bell of Lost Souls is a colossal iron bell that is as massive as a building and adorned with dark runes. It is located at the top of one of the many spires of the Imperial Palace on Terra. Thousand of minarets, towers and spires rise from the Imperial Palace and breach Terra's ever-thinning cloud cover. One, and only one, of these towers stands out from its gold and marbled kindred as it is coloured jet black. It is called the Tower of Heroes. The summit of this looming structure is capped by a bell tower. The belfry itself is the size of a cathedral and houses a single bell forged of unassuming, commonplace metals, marked by the stains and patinas of time's eroding touch. This lone bell is the size of a Titan, and attended by hundreds of men, women and Servitors whose existence is entirely devoted to maintaining the sacred instrument's function.

The Bell of Lost Souls tolls only when the greatest of the Imperium of Man's heroes perish and can be heard by millions of people across the face of Terra. It rarely rings, but when it does, all resident Imperial Palace servants must be evacuated and sealed within reinforced shelters to prevent the annihilation of their eardrums and subsequent death through lung rupture and embolism. Among its many legends is the holiest of all; that when the bell rings, the Emperor hears the sound even in his slumber upon the Golden Throne, and sheds a single tear.

The bell is inscribed across its entire surface with psychically active hexagrammatic runes and its peal is said to sound like the scream of an anguished god, in this case the Emperor of Mankind, mourning the lost lives of his children. Its wailing moan of grief lasts long and reaches the ears of millions, and its tones penetrate the unifying ether of humanity, turning the thoughts of countless billions towards the loss of Mankind as a whole. One of the most well-known, and recent ringings of the Bell of Lost Souls occurred when the Fire Hawks Chapter was declared "Lost to the Warp" in 963.M41 by the High Lords of Terra. That day, the bell tolled 1,000 times, once for each Astartes lost.

There is a special dispensation for the use of the bell concerning the Grey Knights Chapter. As the Emperor's only genetic inheritors amongst the Adeptus Astartes and Mankind’s most valued and incorruptible protectors, the Bell of Lost Souls rings once each time a Grey Knight falls in battle. It is said that this is their reward in place of the recognition they will never receive from a galaxy that does not even know that they exist. A Grey Knight Battle-Brother will stand at the base of the tower in the sacrosant control chamber, surrounded by reverent serfs of the Palace and burning incense, and pull the levers that set the great, arcane mechanisms to work. Minutes later, the bell will toll a certain number of times – once for every fallen brother. All of Terra will then know that the mighty have fallen, and that the Imperium is a darker place because of it.

Operation

When the order comes from the High Lords of Terra or the Emperor Himself, the attendant Palace serfs and Servitors will begin the laborious process of automated lockdown, broadcasting Vox-transmissions to send the belfry attendants into their bunkers. Another serf will start working the controls to awaken the continental communications relays. An overseer will then key in the one hundred and three ciphers required to unlock the safeguards that will allow his menials to access the deeper systems. The wondrous complexity of the Imperium's bureaucracy makes the entire process of ringing the bell take almost eight hours. When all is in readiness, a single servant will have one hand resting on the ornate control console and the other on the lever that will activate the myriad mechanics within the monument. When ordered to do so, the serf grips the lever, whispering a single name as he pulls it. The last lament for the fallen then rings out across Mankind's birth world, ignored by none and heard by all, as humanity's empire mourns another of its fallen heroes.

Sources

• Codex Imperialis (1st Edition)
• Warhammer 40,000 Rulebook (6th Edition), pg. 163
• White Dwarf 99 (US), "Index Astartes, Legion of the Damned"
• The Emperor's Gift (Novel) by Aaron Dembski-Bowden