"You shall make your battle pledges upon this sacred warhammer. This hallowed weapon has fought in the hands of our greatest veterans. It has slain alien beasts and daemons alike. One day, you may be worthy enough to wield it. Until then, you may kneel before it."
The Hammer of Macragge is a potent and revered relic of the Ultramarines Chapter of Space Marines, a millennia-old Thunder Hammer that has long remained aboard the Reclusium of the Battle Barge of the Ultramarines 2nd Company in a shrine of honour. The Hammer of Macragge has been wielded against foes of the Imperium of Man for many millennia, and it contains powerful ancient technology that is little understood in the late 41st Millennium.
The 2nd Company's Ultima Squad swore their battle pledges on the Hammer shortly before their deployment to the Shrine World of Mithron which had come under assault from the Forces of Chaos, including the Chaos Space Marines of the Black Legion. Later, Battle-Brother Proteus confronted a daemon inside the Reclusium of the 2nd Company's Battle Barge and tore the Hammer from its reliquary, using it to banish the daemon back to the Warp, before it could use the Imperial Fists artefact recovered from Mithron, the Liber Mithrus, to open a Warp portal on Macragge itself.