Often, the presence of even a small number of Ultramarines units in a larger military undertaking will ensure the participation of many more Chapters, so highly are the sons of Roboute Guilliman held in their brothers' esteem.When Hive Fleet Behemoth struck the Eastern Fringe, it was the Ultramarines Chapter that turned the tide, even at the cost of the Chapter's entire 1 Company.The culture of the Ultramarines is loosely themed upon the culture of Old Earth's ancient Roman Empire, as exemplified in their Astartes' pseudo-Latin names and their strict adherence to the Codex Astartes, as well as the society of their homeworld of Macragge and the Chapter's method of recruitment.The Ultramarines directly rule the sector of space in the Eastern Fringe known as Ultramar as a fief of the Imperium and their Chapter Master is also considered the Lord of Macragge and the Master of Ultramar.Only a Primarch, a gene-son of the Emperor Himself could have conceived such an undertaking, for the scattered worlds that had survived the Heresy were on their knees, riven with plague and famine and rife for rebellion or invasion.The task was gargantuan, and no mere mortal man could have faced it without going mad.The Ultramarines were originally the XIII Space Marine Legion before the reforms that initiated the Second Founding and reshaped the Imperium after the Heresy on the orders of Guilliman himself.The name "Ultramarines" is a nod to both the Chapter's standing amongst the other Space Marine Chapters and their role as the source for the gene-seed of more Chapters of Astartes than any of the other former First Founding Legions combined.
With the Imperium brought to its knees by galactic civil war, he turned his mind to uniting and codifying the highest echelons of the Imperium's government, imposing order on institutions that had been split asunder by the anarchy of the Heresy.
Across the domains of the Emperor, the Ultramarines are celebrated as heroic, virtuous, and noble defenders of Humanity, their deeds recorded in devotional works the length and breadth of the galaxy.
Even amongst the Space Marine Chapters themselves, the Ultramarines occupy a position of special honour.
The Ultramarines Chapter is at once the exemplar of everything a Space Marine aspires to, and the template by which he acts, fights and worships.
Every Chapter has its own traditions, histories and battle-honours, but the Ultramarines are the standard by which many others, especially those of their genetic lineage, judge themselves and their peers, whether they acknowledge it or not.