Siege Engine

A siege engine is a device that is designed to break or circumvent city walls and other fortifications in siege warfare. Some are operated close to the fortifications, while others attack from a distance. From antiquity, siege engines were constructed largely of wood and tended to use mechanical advantage to fling stones and similar missiles. With the development of gunpowder and improved metallurgical techniques, siege engines became artillery. Collectively, siege engines or artillery combined with the necessary troops and transport vehicles to conduct a siege are referred to as a ‘siege-train.’

The earliest engine was the battering ram, developed by the Assyrians, followed by the catapult in ancient Greece. The Spartans used battering rams in the Siege of Plataea in 429 BCE, but it seems that the Greeks limited their use of siege engines to assault ladders, though Peloponnesian forces used something resembling flamethrowers. The Carthaginians used siege towers and battering rams against the Greek colonies of Sicily.

The first two rulers to make use of siege engines to a large extent were Philip II of Macedonia and Alexander the Great. Their large engines spurred an evolution that led to impressive machines, like the Demetrius Poliorcetes’ Helepolis (or ‘Taker of Cities’ of 304 BCE: nine stories high and plated with iron, it stood 40 m (125 ft) tall and 21 m (60 ft) wide, weighing 180 tons. For sea sieges they used sambuca, giant ladders, hinged and mounted on a base mechanism and used for transferring marines onto the sea walls of coastal towns. They were normally mounted on two or more ships tied together and some included shields at the top to protect the climbers from arrows.

The earliest documented occurrence of ancient siege artillery pieces in China was the levered principled traction catapult and an 8-foot high siege crossbow written about by Chinese philosopher, the Mozi, in the 4th century BCE. Medieval designs include a large number of catapults such as the Mangonel, Onager, the ballista, the traction trebuchet (first designed in China in the 3rd century BCE and brought to Europe in the 4th century CE), and the counterweight trebuchet (first described by Egyptian military scholar, Mardi bin Ali al-Tarsusi in the 12th century). These machines used mechanical energy to fling large projectiles to batter down stone walls. Another weapon was the petard, an explosive device designed specifically for breaching gates and walls. The petard had to be placed directly against the surface of the fortress.

A typical military confrontation in medieval times was for one side to lay siege to an opponent’s castle. When properly defended, they had the choice whether to assault the castle directly or to starve the people out by blocking food deliveries, or to employ war machines specifically designed to destroy or circumvent castle defenses. Other tactics included setting fires against castle walls in an effort to decompose the cement. Another indirect means was the practice of mining, whereby tunnels were dug under the walls to weaken the foundations and destroy them. A third tactic was the catapulting of diseased animals or human corpses over the walls in order to promote disease which would force the defenders to surrender, a primitive form of biological warfare.

With the advent of gunpowder, firearms such as the arquebus and cannon—eventually the mortar and artillery—were developed. These weapons proved so effective that fortifications, such as city walls, had to be low and thick, as exemplified by the designs of French military engineer, Vauban. The development of specialized siege artillery, as distinct from field artillery, culminated during World War I and II. During the First World War, huge siege guns such as Big Bertha were designed to see use against the modern fortresses of the day.

The apex of siege artillery was reached with the German Schwerer Gustav gun, a huge 800 mm caliber railway gun, built during early World War II. It was initially intended to be used for breaching the French Maginot Line of fortifications but was not finished in time and (as a sign of the times) the Maginot Line was circumvented by rapid mechanized forces instead of breached in a head-on assault. The long time it took to deploy and move the modern siege guns made them vulnerable to air attack and it also made them unsuited to the rapid troop movements of modern warfare.

Siege weapons are now considered obsolete owing to the effectiveness of aircraft-delivered munitions and cruise missiles, which have made defensive area fortifications obsolete. The only cost effective static defensive structures are now deep bunkers used for military command and control. Even these fixed assets are of questionable value as it appears that the most survivable command and control of mobile defensive forces (such as modern tactical and strategic aircraft, mechanized cavalry and mechanized infantry) is through decentralized command and the use of mobile command centers.


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