It acted as guardian of trade routes , policed Bedouin tribes and was a source of troops for the Byzantine army .
Geographically , it occupied much of Syria , Palestine and the northern Hijaz as far south as Yathrib ( Medina ) .
Syria acted as guardian of trade routes , policed Bedouin tribes and was a source of troops for the Byzantine army .
Geographically , it occupied much of Syria , Palestine and the northern Hijaz as far south as Yathrib ( Medina ) .