Only in Crusader Kings II could a horse rise to power and, after decades of war and conquest, restore the might of the Roman Empire. Normally CKII is a very serious game, as much a simulation of bloodthirsty medieval politics as it is a strategy game, but developers Paradox aren't without a sense of humour.
A while back they slid Glitterhoof, an actual horse, into the game as one of your councillors (a joke related to some DLC called "Horse Lords"). It was amazing, but also limited, because unlike the humans in the game Glitterhoof couldn't be married off to make babies and propagate a whole dynasty of royal horses.
When the patch added Glitterhoof as an actual in-game character I'd assumed that the horse trait meant console commands were the only way to interact with him- but, as another user figured out in this thread, there's a hole in it since it doesn't block him being nominated as a bishop (this bishop must also be count-level or higher). By nominating him and waiting for the current bishop to die he should spawn some horse culture/ethnicity courtiers of his own (and if you want to be sure of this you can grant him independence)- except they won't have the horse trait. After that you can grant them land and marry these new courtiers freely, so I just bred my rulers with them until I got an heir with horse ethnicity.
If that paragraph doesn't sell you on Crusader Kings II, then I just don't know how to help you.
Anyway, taking advantage of that loophole, nanomaster ran a game where, through a little trial, error and insanity, he managed to elevate Glitterhoof to a position of power. A CKII quirk then let Glitterhoof import a bunch of other horse characters to serve him, and voila, Europe has its own breeding stock of horse lords.
What happens next is difficult to explain to non-players, but the gist is that, through careful knowledge of how the game's various religious and political systems work, nanomaster was able to seed Europe with a whole caste of ruler horses, before taking one of their descendants and managing what no actual Emperor, King or General was ever able to accomplish: the restoration of the Roman Empire.
Rainbow Dash, born in 896, would rise to become Empress, directly leading her armies in a conquest of North Africa, the Middle East and the Mediterranean. Oh, and while she was at it, she also unified the great schism of the Christian faith.
I honestly don't know what's more impressive here. The exploitation of the loophole or the skill required to take that loophole and do something so cool with it. I've played this game for way too long, and couldn't dream of pulling off something so ambitious and well-timed.
The complete account of this dynasty has been recorded here, and it's required reading for anyone who is into Crusader Kings II. Or good horse puns.