Any of several flammable materials used in warfare in ancient and medieval times. Ancient writers refer to flaming arrows, firepots, and such substances as pitch, naphtha, sulfur, and charcoal, but true Greek fire was evidently a petroleum-based mixture. It was evidently invented during the reign of Constantine IV Pogonatus by a Greek-speaking Syrian refugee from the Arab conquest of Syria. It could be thrown in pots or discharged from tubes and was difficult to put out when alight.