[quote=@babbysama]
I was thinking about using the House of Karen, one of the Seven Parthian Clans,
[/quote]

I was hoping somebody would take up a Parthian family. Go for it.

[quote=@babbysama]
Also, what year will we be starting in, or has that been decided yet? 
[/quote]

634 AD

[quote=@Nilesapa]
Given the rise of islam happened in the context of a still prominent Roman Empire, wouldn't this cause serious butterflies to the faith
[/quote]

It could, but i've chosen not to change it for the sake of simplicity. Like any alternate history, i'm just tweaking what I want to really. As for the stability question, the Roman Empire survived but it isn't necessarily stable. The Empire would still be experiencing the teetering internal cohesion it had been experiencing since the Severans. In the real world, the Eastern Empire sort of played at being the total Emperor for a few centuries, and many of the Germanic Kings were at the very least playing lip service to the Imperial title. In doing so, the Germanic Kings gained legitimacy among their still often Roman subjects, and the Emperor got to pretend that the Germanic Kings were just ruling in his stead.

In this scenario, however, the Roman Empire is physically stretched across this land. They have to pay to defend it, to man the borders, and when there are border incursions they have to fight them off. We can just as easily say that the bloody wars with the Parthians also still went on, meaning that both Empires will be somewhat exhausted.

But of course it is alt history. Who the hell knows how we will end up letting this play out.  

[quote=@Nilesapa]
I have interest, but unsure where to go.  Although I do ask, are Knights a thing here?
[/quote]

More or less. There would be no chivalric code or knightly orders of course, but the concept of giving land to your household guard or heavy cavalry wouldn't be strange. In some sense, Knighthood derived from how important heavy cavalry in the period of the late Roman Empire, and it shares a sort of mixed heritage with the Germanic household guard and the Roman equestrian class. 

And I personally will probably use this term, and a few other anachronistic terms, to put some emphasis on how we are evolving out of antiquity and entering the medieval world.