Complex sentence: The initial core of the structure was erected in the 10th century by the Normans in what for them was a typical motte and bailey structure and, during the Crusades, it was a used as a hostel for soldiers leaving for the Holy Land.
Split into simpler sentences: The initial core of the structure was erected in the 10th century by the Normans as a motte and bailey structure. During the Crusade period, it was a used as a hostel for soldiers leaving for the Holy Land.