Overview of Mithras

In our timeline, Rome came dangerously close to falling in the 3rd century. In the book's timeline, Emperor Aurelian never had the chance to rise before the Mithran cult became militant and took over the empire, turning it into a theocracy within a few generations. Slowly, they relinquished territory to gain better stability with this gargantuan change in religion and society.
Over the years, the borders above the alps rarely changed, nor did they invade many other places other than the new world where their wealth ultimately came from in the form of slaves, mining, cocoa, and sugarcane along with other smaller commodities.
Other countries first saw them as a threat during the silent war in the Blue Isles, where the Celti-pact backed Palmyrenes. Both underestimated Mithra's might.

Mithras is a slave society with a strict hierarchy. Servus, who outnumber their masters 20 to 1, make up the majority of the population and perform most of the menial tasks and basic fighting while the aristocratic elite enjoy a life of opulence and military service against their old rival: Azteca. However, they have set their sights on breaking the Celti-pact, namely Kymbri- their chief rival in technology and military might.

While everyone is forced to worship Mithras, there are a few factions in this theocracy. First, it is not ruled over by an all powerful theocrat, but by a senate and an inner concilium. One cannot help but compare this structure to Kymbri's cened and Alundai cened, except that the Mithrans have no central figure since their God is the center of all things.
 
The worship of Mithras is very different than what we used to know. He is the only God that they believe in and his word is might. The killing of the bull represents Mithras overtaking the entire world, hence, most believe that their ultimate destiny is to push Mithras and to conquer other lands. There is no holy book as we might think. While there are a few stories about Mithras, the writings mostly contain tenets and the ways of being.