[quote=@Dinh AaronMk]
The thing with Caliph to remember though is that the title effectively means "successor" and is designate to those chosen to be the successors of Muhammad. So if during the time of Muhammad there'd be no "Caliph" since there's no one to succeed him and his mission. But if during the Rashidun that followed him, there'd be Caliphs. Elected Caliphs prone to being murdered because tribe dies hard.
[/quote]

If we are RPing in the time in which the Islamic invasion is starting into Syria, it would be during the Rashiduns. 

[img]https://oneway2day.files.wordpress.com/2011/08/islamic-early-conquests-map.jpg[/img]

Looking at that, an RP during Mohammeds lifetime would be relatively bland if we are focusing on the Roman world. Especially since the conquests of Mohammed are difficult a draw a border for, since most of that land was nomad filled deserts where the claim is based on where the Muslim tribes happened to be concentrated.