|This article is about the Imperial symbol. For other uses of Aquila, see Aquila (disambiguation).|
Aquila served as a Sergeant of the Ultramarines during the Battle of Calth. He, along with his Company, were stationed at the city of Ithraca. During the initial bombardment and assault, the entire Ultramarines Company was destroyed save Aquila and two others. Aquila decided the best course of action would be to proceed to a downed Titan lander, which was being used as both a strong point and evacuation center for the city's reeling defenders.
During the journey through Ithrica, Aquila and his men happened upon a young woman, Varinia, and her week-old son, Pexcillius. Initially wanting to leave them behind, Aquila was convinced by his brother Gaius to bring the two along with them in hopes of finding Varinia's husband Quintus and securing their passage off-world. Gaius pointed out that their fallen Captain was also named Pexcillius and he wouldn't have thought twice about taking the young woman with them.
Varinia would later be mortally injured by shrapnel and Aquila suggested killing her to spare her the suffering. Gaius was about to defend their choice to save the woman when Varinia snapped at Aqualia, stating that the people of Calth never gave up and that if she, a normal human who was bleeding to death could find the strength to carry on, then a battle-hardened Space Marine had no business giving up. Shamed by the woman's passion, Aqulia ordered Gaius to carry the injured woman and they continued on.
Soon the group found themselves in the cross-fire between a Traitor Warhound of the Fire Masters and a loyalist Reaver Titan of the True Messengers. A stray volley from a Volcano Cannon blasted apart the building the Ultramarines had taken shelter in. The roof collapsed and Gaius sacrificed himself, throwing himself over Varinia and her child to save them from falling masonry. Varinia bled to death soon after. Aquila was moved by the sacrifice of his brother and realised that even though he himself was already dead, he had a duty to protect the innocent and suffer so they did not have to. Aquila scooped up the still-alive Pexcillius and promised the infant he would one day grow up and avenge the death of his mother and might even march in the plate of a Space Marine.
During the later Horus Heresy, the Ultramarines rushed to Terra to intervene on the Emperor's side during the Battle of Terra, but arrived too late to prevent the Emperor's incapacition by Horus. Although the Traitor Legions were ultimately routed, all the Ultramarines felt their failure keenly. Aquila, in particular, was inconsolable and desperate to atone in some way.
When the Ultramarines were divided into Successor Chapters, Aquila founded the Doom Eagles chapter, which embraced his sense of fatalism. All Doom Eagles accept that death is inevitable, and that every mission on behalf of the Imperium must be pursued with the same fervour, believing that the only important thing is to be of service to the Imperium and its peoples before one's life is spent.