Of the many campaigns during the Middle Ages, few are as remarkable or seemingly impossible to win at the start as the First Crusade (1095-99), and the true crowning achievement of that crusade, which resulted in two centuries of Western European Christian states in the Middle East and the permanent firing of the European imagination, was the conquest of Jerusalem on July 15, 1099 after three weeks of siege. That victorious siege came four years after the call for a crusade first went out, and had the Crusaders not taken Jerusalem, the First Crusade would not likely have been followed by any more and the campaign might have been no more than an historical footnote of what could have been.

As it turned out, the siege of Jerusalem and the crusade as a whole says much about the first major clash of Western and Eastern military tactics after the fall of the Roman Empire, as well as the power of faith and even fanaticism to motivate people beyond ordinary human endurance. For better and worse, the siege and fall of Jerusalem to the Crusaders has become a fundamental piece in the current view of the West in that part of the world. Indeed, to this day, the First Crusade remains a polarizing event, even among modern historians. For some, the Crusaders were heroes and saints, and for others they were devils who disrupted the peaceful local sects of Muslims, Jews, and Christians, establishing an alien colony that heralded modern European imperialism. In fact, the First Crusade is a good example of why it is unwise to choose sides in history, because neither side was correct and the situation was highly complex.