[oriental sore]. Conditions in the Eastern Mediterranean were unfamiliar and hostile to ill-equipped European crusaders. The boil was the outward sign of a disease known to modern medicine as leishmaniasis. It was the consequence of a parasitic infection, with unpleasant symptoms of boils, ulcers and liver damage; it was frequently fatal (disease was a more effective killer of crusaders than the Saracens). Aleppo was in today's north Syria. Then it was an important garrison town of the Muslim forces.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.