Historical Incendiary Devices
Before the advent of high explosives and large armies, fire played a massively important role in warfare. Conquests relied largely on destroying the enemy’s infrastructure and sapping his morale; one of the easiest ways to accomplish these goals was to burn his cities. Indeed, fire was a dream weapon for invaders; its destructive effects could be brought to bear on a target with a minimal amount of time and effort, but it could not be extinguished without a massive diversion of resources on the defenders part. Further, fire could not be used against the invading forces to much effect.
A mixture of pitch, naphtha, sulfur, and petroleum which bursts violently into flame; it is extremely difficult to extinguish. Invented by the greeks in (c. 1200 BC), this technology has been used in countless military campaigns, most recently in the American Civil War. Greek fire has been used by besieging forces to ignite the walls of resilient cities. Also, Geek fire was an excellent naval weapon (during the age of wooden navies) because it could float on water while burning, and could therefore be used to set fire to enemy ships from a distance.
This simple technology is of immemorial antiquity, presumably developed shortly after the advent of archery as the first stand-off incendiary weapon.
Trebuchet and Catapult Munitions
Medeival armies would load their siege engines with Greek Fire or flaming oil pots; these weapons were presumably the first to carry not only flame but a large quantity of highly flammable material into the target.
Perhaps the most popularly accessible of incendiary weapons, Molotov cocktails (named after a soviet foreign minister) are made by stuffing an oil-soaked rag into the mouth of a bottle partially filled with a flammable liquid (usually alcohol, but sophisticated versions have used gasoline thickened with soap). When the weapon is used, the rag is lit on fire and the entire assembly is thrown through the air at the target. If all goes to plan, the bottle shatters upon impact with the target spreading flammable materials over it; the flaming rag then ignites the flammable liquid, causing a rapidly spreading fire.