Jerusalem was taken by the European "liberators" in July of 1099, in what would later be known as the First Crusade. A month later, Ascalon fell as well.
Both of these events of world history are a part of the Toobworld timeline officially, as a fictional TV character took part in both campaigns: Brother 'Cadfael', whom the audience meets forty years later as a murder-solving monk at Shrewsbury Abbey in Shropshire.
By the way, the term "crusade" would not be coined until sometime in the 13th Century to describe these waves of invasion into the Holy Land. And therefore any use of the word by Brother Cadfael and others in those episodes would be an anachronism. The only way out is that once again, here is a difference between the real world and Toobworld, and the word "crusade" must have been coined far, far earlier in TV Land.