Answer:
The combustible mixture commonly used for military purposes during the Middle Ages was called Greek fire. It was a highly flammable liquid that was projected onto enemy ships or troops, causing significant damage and destruction. The exact composition of Greek fire is not known, as it was a closely guarded secret of the Byzantine Empire, which developed and used the weapon extensively. However, it is believed to have included ingredients such as petroleum, quicklime, and sulfur, which made it highly combustible and difficult to extinguish.