Take a look at the supplement "Mythic Europe" for Ars Magica released by White Wolf in '92. It has lots of interesting background material.
Or you could wait for the to-be-released book about the Levant.
The First Crusade was launched to retake the city of Christ after the Seljuk Turks started harassing pilgrim in 1071. Pope Gregory VII wanted to launch a crusade in 1074, but it was his successor Pope Urban II that brought the plans to fruition.
Numerous cities was sacked or surrendered, among them Jerusalem which was the place of a horrendous slaughter of both jews and saracens. After the crusade, several christian states were created: Kingdom of Jerusalem, Principality of Antioch and the Counties of Edessa and Tripoli.
As for adventures here, it all depends on what you have in mind: epic or not, does divine intervention exist etc.
An example: The party is called upon by sir Godfrey to find the Holy Lance, with which a roman soldier cut christ when he was on the cross. The lance is rumoured to exist within Antioch. When the lance is paraded around the walls of Jerusalem, it is said this divine relic will bring the holy warriors to victory.
In reality, it is an infernal relic, which will actually raise the attackers ferocity and bloodlust, thus being behind the following slaughter.
Was it something like this you wanted?
