Early thermal weapons

thumb|right|300px|The Siege and Destruction of Jerusalem by the Romans Under the Command of Titus, A.D. 70, by [[David Roberts (painter)|David Roberts (1850), shows the city burning]]

Early thermal weapons, which used heat or burning action to destroy or damage enemy personnel, fortifications or territories, were employed in warfare during the ancient and post-classical periods (approximately the 8th century BC until the mid-16th century AD).

Incendiary devices were frequently used as projectiles during warfare, particularly during sieges and naval battles: some substances were boiled or heated to inflict damage by scalding or burning; other substances relied on their chemical properties to inflict burns or damage. These weapons or devices could be used by individuals, thrown by siege engines, or utilised as army strategy. Incendiary mixtures, such as the petroleum-based Greek fire, could be launched by throwing machines or administered through a siphon. Sulfur- and oil-soaked materials were sometimes ignited and thrown at the enemy, or attached to spears, arrows and bolts and fired by hand or machine.

The simplest and most common thermal projectiles were boiling water and hot sand, which could be poured over attacking personnel. Other anti-personnel weapons included the use of hot pitch, oil, resin, animal fat and other similar compounds. Smoke was used to confuse or drive off attackers. Substances such as quicklime and sulfur could be toxic and blinding.

Fire and incendiary weapons were also used against enemy structures and territory, sometimes on a massive scale. Large tracts of land, towns and villages were frequently ignited as part of a scorched earth strategy. Some siege techniques—such as mining and boring—relied on combustibles and fire to complete the collapse of walls and structures.

Towards the latter part of the period, gunpowder was invented, which increased the sophistication of the weapons, starting with fire lances, which led to the eventual development of the cannon and other firearms. Development of the early weapons has continued ever since, with modern war weapons such as napalm, flame throwers, and other explosives having direct roots in the original early thermal weapons. Fire-raising and other destructive strategies can still be seen in modern strategic bombing.

"Fire and sword"

The destruction of enemy possessions and territory was a fundamental strategy of war, serving the dual purpose of punishment and deprivation of resources. Until the 5th century BC, the Greeks had little expertise in siege warfare and relied on a strategy of devastation to draw the enemy out; they destroyed crops, trees and houses. Centuries later, the Byzantines recommended this strategy, even though they had developed siege technology.

Fire was the easiest way of harrying and destroying territories, and could be done easily and quickly by small forces. It was a strategy put to good use by the Scots during the Wars of Independence; they repeatedly launched raids into northern England, burning much of the countryside until the whole region was transformed.

The tactics were replicated by England during the Hundred Years' War; fire became their chief weapon as they laid waste to the French countryside during lightning raids called chevauchées, in a form of economic warfare. One estimate records the destruction of over 2000 villages and castles during one raid in 1339.

As well as causing the destruction of lands, food and belongings, fire could also be used to divert manpower. 13th century Mongol armies regularly sent out small detachments from their main forces to start grass fires and fire settlements as diversions.

Devastation by fire was not only used as an offensive tactic; some countries and armies employed "scorched earth" policies on their own land to deprive invading armies of all food and forage. King Robert the Bruce of Scotland reacted to the English invasion of 1322 by launching punitive and diversionary chevauchées into north-west England, then retreating to Culross, burning as he went the Scottish lands which lay in the path of the English army. The English ran out of food and had to abandon the campaign.

Such acts of aggression were not limited to wars against territorial enemies, but could form part of the strategies of conquest, subjugation and punishment of rebellion. Alexander the Great suppressed a revolt in Thebes, Greece in 335 BC, after which he ordered the city to be torched and laid waste. Alexander ordered (or allowed) a similar arson at Persepolis in 330 BC. It was a policy which was repeated throughout the period. William the Conqueror, following his conquest of England in the 11th century, asserted his control of Northumbria by destructive campaigns throughout the region: "He ordered that crops and herds, tools and food should be burned to ashes. More than 100,000 people perished of hunger", reported Orderic Vitalis, a contemporary chronicler. It was a scene repeated the following century, during The Anarchy of Stephen of England's reign. Civil war erupted between Stephen's supporters and those of the Empress Matilda, a rival claimant for the throne. The Gesta Stephani tells of the deeds of one of Stephen's supporters, Philip of Gloucester, by describing how he "raged in all directions with fire and sword, violence and plunder", reducing territory to "bare fields and dreadful desert".

Techniques of use

thumb|[[Normans use torches to fire the wooden keep on a motte at Dinan, 1064, Bayeux Tapestry]]

At the simplest level, fire itself was used as a weapon to cause large-scale destruction, or to target specific enemy positions or machinery. It was frequently used against siege engines and wooden structures. Incendiary weapons could be used to set fire to towns and fortifications, and a wide range of thermal weapons were used against enemy personnel. Some armies developed specialised "fire-troops". By 837, many Muslim armies had groups of "naffatin" (fire archers), and when the Mamluk Sultanate raised a fleet for an attack on Cyprus (1425) they had "nafata", or fire-troops.

Simple fire-raising

The burning of enemy positions and equipment was not necessarily a complicated procedure, and many fires were set by individuals using common materials. When William of Normandy's army besieged Mayenne in 1063, they shot fire into the castle to panic the garrison, while two boys stole into the castle in order to start a fire within. The garrison surrendered.

Besieged forces would sometimes launch sorties in an attempt to fire the attackers' camps or equipment. When Hugh Capet besieged Laon in 986–987, his troops became drunk one night, and Duke Charles's men sallied forth and torched the camp, forcing Hugh to abandon the siege.

The besieged were not the only ones who might fire siege equipment; when Frederick Barbarossa abandoned his siege of Alessandria in 1175, he burned his own camp and equipment.

However, like all weapons, fire-raising had its own dangers. In 651 Penda of Mercia attempted to win Bamburgh Castle by building a pyre at its base from planks, beams, wattle and thatch. The wind changed direction and the fire blew back on Penda's men, who had to abandon the attack. This fortuitous wind-change was credited to Saint Aidan, who saw the smoke from the Farne Islands and prayed for the defenders.

Throwing machines

thumb|right|1869 engraving showing a 13th-century [[trebuchet launching an incendiary missile]]

Various throwing machines were in use throughout the classical and medieval periods. Generally referred to as "artillery", these engines could hurl, fire or shoot missiles and most could be used or adapted for throwing thermal weapons, by attacking and defending forces. Barrels, fire pots and other breakable containers of pitch, Greek fire, and other incendiary mixtures could be thrown; other machines fired arrows and bolts, which could be ignited, or adapted to carry flammable mixtures. From the 12th century, Muslims in Syria were using clay and glass grenades for fire weapons, thrown by machines.

Most of the terms used for throwing machines were vague, and could refer to different engines, all of which went through changes and developments over the period. Among the most common were the ballista, mangonel and trebuchet. The ballista was similar in form to a crossbow, though much larger, and used a string-winding mechanism to fire a missile or bolt placed in a groove. Other giant crossbows were used throughout the period, and an "espringal", based on the ballista, which threw large bolts, was developed in the 13th century. Torsion-powered arrow firers had been used from 400 BC, and were adapted for stones. The trebuchet was an advanced development of the 12th or 13th century, which used a counter-weight to power the throwing arm, and was the major siege engine until the cannon became widespread.

As the tunnels were constructed, they were generally supported by wooden beams and posts. Once the mine had been finished, the internal space was filled with combustibles, such as brushwood, firewood, resin, and other incendiary substances; once ignited, these would burn the supporting props, causing the mine to collapse, bringing down with it the structures lying above. From the 15th century, gunpowder was also used, although the aim remained to burn the props.

Defenders might sometimes dig counter-tunnels in order to reach the enemy's mines and launch an attack; frequently thermal weapons were used to drive the besiegers from the tunnels.

Rather than undermining a structure, some besiegers used borers to drill holes in the outer walls in an effort to destroy them; such methods were more effective than rams on brick walls (which tended to absorb the shocks from the ram). Borers differed in size and mechanism, but a typical machine was made from a log of wood, tipped with iron and supported and driven by windlasses or ropes.

Fire ships

thumb|right|upright|Chinese fire ships from the [[Wujing Zongyao military manuscript, 1044, Song dynasty]]

Fire ships were used on several occasions throughout the period. In 332 BC Alexander the Great laid siege to Tyre, a coastal base of the Phoenicians. In order to bring his siege engines within range, Alexander ordered the construction of moles. The Tyrians responded by attacking the first mole with a large fireship, which destroyed it. A large horse transport ship was packed with cedar torches, pitch, dried brush and other combustibles; above this were suspended cauldrons of sulfur, bitumen and "every sort of material apt to kindle and nourish flame". This was towed to the mole, and lit by the Phoenicians before they jumped overboard and swam away.

Another example occurred during the 886 Siege of Paris, when the Vikings filled three warships with combustible material and pulled them upriver in a failed attempt to destroy the Franks' fortified bridges. Fire ships containing straw and powder were also used during the Chinese Battle of Lake Poyang in 1363.

Other methods

Often ingenious methods were developed for administering the weapons. The 10th-century Olga of Kiev is reported to have tied burning tinder to birds which, when released, flew back to their nests in the hostile town and set them alight.

Siege towers and ladders could be fitted with a long, narrow tilting beam at the top, gouged with a groove, so that hot oil and water could be poured down on the enemy defenders during an escalade.

During an attack, castle or fortification defenders could launch or pour the substances on the heads of attackers below. This could be done over the battlements, but also through purpose-built holes such as machicolations and murder-holes. During night attacks, defenders could drop lighted bundles over the walls so the enemy could be seen; Chinese and Muslim sources also describe the light gained by torches hung on the walls.

Use against stone castles

Stone castles were susceptible to fire, since they contained many combustible materials. In 1139, Henry de Tracy forced the surrender of Torrington Castle by the simple expedient of tossing lighted torches through the keep's loopholes.

Stone was also susceptible to intense heat, which would cause it to crack and collapse. Byzantine sources recorded the demolition of stone structures caused by placing clay pots of burning charcoal at the base of walls moistened with vinegar or urine,

Stone castles sometimes offered other inflammatory targets. During the Crusades, Muslim defenders frequently hung bundles of straw against their walls as buffers against stones and rams; in turn, the Crusader archers would set these alight with flaming arrows.

Defense against thermal attack

Defense from thermal weapons and fire attacks was usually water or other liquids such as urine; hides were soaked and draped over vulnerable wooden hoardings and siege engines, vats and barrels of liquid were collected and stored by defenders and attackers. Wooden structures were frequently soaked in alum to increase their fire resistance. Throughout the period, sacks or nets might be filled with vinegar-moistened chaff, seaweed or wet moss and hung on the exterior. The wooden siege engines of the Crusaders were vulnerable to attack from the Byzantine and Muslim fire-weapons, so the troops inside siege towers kept stores of water and vinegar.

During the High Middle Ages, the majority of Poland's castles were still made of wood, so uncut stone was frequently added to the front to improve their fire defences.

Both attackers and defenders needed to be prepared for incendiary and thermal attack. When the Athenians besieged Syracuse in 416 BC they lost many siege engines to fire. The Syracusan ruler Dionysius I must have taken note of this success, for when he laid siege to Motya in 398 BC he organised special fire "brigades", who successfully doused the fires when his siege engines were bombarded.

Types of weapons

Flaming arrows, bolts, spears, and rockets

thumb|300px|Two fire arrows (crossbow bolts). Southern Germany, ca. 15th century, with preserved incendiary mixture of saltpeter, charcoal, sulphur and textile on the shaft.

Lit torches (burning sticks) were likely the earliest form of incendiary device. They were followed by incendiary arrows, which were used throughout the ancient and medieval periods. The simplest flaming arrows had oil- or resin-soaked tows tied just below the arrowhead and were effective against wooden structures. More sophisticated devices were developed by the Romans which had iron boxes and tubes which were filled with incendiary substances and attached to arrows or spears. These arrows needed to be shot from loose bows, since swift flight extinguished the flame; spears could be launched by hand or throwing machine.

Flaming arrows required the shooter to get quite close to their desired target and most will have extinguished themselves before reaching the target. In response, another form of fire arrow was developed which consisted of curved metal bars connecting a tip and hollow end for the shaft. The resulting cage was filled with hot coals or other solid object which could be fired from a much stronger bow or ballista without fear of extinguishing and would be used to ignite straw or thatch roofs from a safer distance.

Flaming arrows and crossbow bolts were used throughout the period. Fifteenth-century writer Gutierre Diaz de Gamez witnessed a Spanish attack on the Moorish town of Oran in 1404 and later described how "During the most part of the night, the galleys did not cease from firing bolts and quarrells dipped in tar into the town, which is near the sea. The noise and the cries which came from the town were very great by reason of the havoc that was wrought."

Anna Komnene records that at the 1091 Battle of Levounion, lighted torches were fixed to spears.

The Chinese Song dynasty created fire arrows arrows with pouches of gunpowder, which were launched en masse through platforms, and later created rockets such as the huo long chu shui, a multistage rocket used in naval combat. Primitive rockets made from bamboo and leather were used by the Mongols, under Genghis Khan, but were inaccurate.

A long iron crossbow-bolt probably designed to carry a fire cartridge was found in a 13th–14th-century castle in Vladimir, Russia. Such large machine-thrown bolts were ideal for incendiary weapons. The Mongols used an "ox-bow" machine to throw bolts which had been dipped in burning pitch, with a range of 2500 paces.

During the British Civil Wars (mid-17th century in Great Britain), both the Parliamentarian and Royalist armies used various incendiary devices to attack enemies and destroy property that might be used for military purposes, according to historian Stephen Porter in Destruction in the English Civil Wars. The flaming arrow attack was used to set fire to buildings at a distance. An arrow with a flammable substance attached to the shaft, close to the tip, was shot from a bow or short-muzzled musket. Such arrows shot from a musket had their feathers removed, to fit inside the muzzle, and were called fire-darts. These devices were cheap to make and easy to prepare. Although used infrequently during the wars, the flaming arrows and darts proved to be destructive. The Royalists shot flaming arrows into the thatched homes in the suburbs of Chester causing extensive damage. Lyme Regis was partly razed using flaming arrows.

Pyrphoros/Pyrphorus

According to Polybius, the ancient Rhodian admiral Pausistratus used a device called πυρφόρος (pyrphoros/pyrphorus) designed to project fire onto enemy ships while it safely distant from the user's own vessel. The apparatus consisted of a funnel-shaped container (scoop or basket) filled with combustible material, suspended from the end of a pole by an iron chain that projected from the prow. These poles were supported by ropes running along the inner sides of the hull, allowing the funnel to extend outward on either side of the bow. Because the funnel was angled away from the ship, fire could be discharged into an enemy vessel during a charge or while passing alongside, without risking accidental ignition of the user’s own ship.

Greek fire

thumb|right|Depiction of Greek fire in the 12th century [[Madrid Skylitzes]]

thumb|Hand grenades filled with [[Greek fire; surrounded by caltrops (10th–12th centuries National Historical Museum, Athens, Greece)]]

Greek fire was one of the most effective thermal devices, although it was extremely dangerous for the users. Early experiments by the Byzantines in the 6th century used a mixture of sulfur and oil, which would have been terrifying if not destructive. It probably had regional variations; the Islamic derivative was known as "naft" and had a petroleum base, with sulfur; the Persian word for "petroleum" is نفت (naft).

The combustible liquid could be shot from catapults, and would burst into flames on impact. It remained effective at sea even after its use had declined on land after the 13th century. Saltpetre (also called "Chinese salt") was added to the mixture in the Islamic world, and China developed a dry saltpetre mixture in the 12th century, which eventually became gunpowder. Both the Parliamentarian and Royalist armies used Greek-fire-like petroleum-based incendiary devices known as "wildfire" during the British Civil Wars. Zhang Xie in Dong Xi Yang Kao (1618) mentioned that city of Palembang, which has been conquered by Javanese, produces the furious fiery oil (ming huo yu), which according to the Hua I Kao is a kind of tree secretion (shu chin), and is also called mud oil (ni yu). Zhang Xie wrote:<blockquote>It much resemble camphor, and can corrode human flesh. When ignited and thrown on water, its light and flame become all the more intense. The barbarians use it as a fire-weapon and produce great conflagrations in which sails, bulwarks, upperworks and oars all catch fire and cannot withstand it. Fishes and tortoises coming in contact with it cannot escape from being scorched.</blockquote>Because there was no mention of projector pump, the weapon is probably breakable bottles with fuses. Moreover, it could be dangerous and volatile. Since the smoke point of oil is lower than its boiling point, the oil was only heated and not boiled.

Pouring-oil was used in historic battles, and Josephus described its use at Jotapata in AD 67, saying "the oil did easily run down the whole body from head to foot, under their entire armour, and fed upon their flesh like flame itself."

Oil was usually used to create incendiary devices. The Roman-Byzantine armies of the 6th century created "fire-pots", oil-based incendiary weapons which could be launched by hand or with ballistae.

During the siege at Montreuil-en-Bellay in 1147, a mixture of oils from nuts, cannabis and flax, was heated in iron containers, launched by mangonel, and burst into flames on impact. The Chinese made early grenades out of oil-soaked hemp and cotton, which were ignited and thrown by mangonels.

Another use of oil can be seen in the naval battle of La Rochelle during the Hundred Years' War; the Castilians sprayed oil on the decks of English ships then ignited it by shooting flaming arrows down.

Water, sand and other heated missiles

Hot oil was considerably less common than boiling water or heated sand, which were cheap and extremely effective; even "dust from the street" could be used. These would penetrate armour and cause terrible burns. Sand, especially, could work its way through very small gaps in armour.