Siege warfare in the context of "Battle of Alesia"

A siege engine is a device that is designed to break or circumvent heavy castle doors, thick city walls and other fortifications in siege warfare. Some are immobile, constructed in place to attack enemy fortifications from a distance, while others have wheels to enable advancing up to the enemy fortification. There are many distinct types, such as siege towers that allow foot soldiers to scale walls and attack the defenders, battering rams that damage walls or gates, and large ranged weapons (such as ballistas, catapults/trebuchets and other similar constructions) that attack from a distance by launching heavy projectiles. Some complex siege engines were combinations of these types.

Siege engines are fairly large constructions – from the size of a small house to a large building. From antiquity up to the development of gunpowder, they were made largely of wood, using rope or leather to help bind them, possibly with a few pieces of metal at key stress points. They could launch simple projectiles using natural materials to build up force by tension, torsion, or, in the case of trebuchets, human power or counterweights coupled with mechanical advantage. With the development of gunpowder and improved metallurgy, bombards and later heavy artillery became the primary siege engines.

The Battle of Salamis in 306 BC took place off Salamis, Cyprus between the fleets of Ptolemy I of Egypt and Antigonus I Monophthalmus, two of the Diadochi, the generals who, after the death of Alexander the Great, fought each other for control of his empire.

Cyprus had been seized by Ptolemy, and was used as a base for operations against the Antigonid territories in Asia Minor and the Levant. In 306 BC, Antigonus sent his son Demetrius to invade the island, which was defended by Ptolemy's brother Menelaus. After landing on the northeastern part of the island, Demetrius marched to Salamis, defeated Menelaus in a battle, and laid siege to the city. This was the first time where Demetrius demonstrated his flair for siege warfare, which would later earn him the sobriquet Poliorcetes, "the Besieger". Nevertheless, Menelaus held off Demetrius' attacks until the arrival of reinforcements. Ptolemy led a large-scale rescue expedition in person, hoping to catch Demetrius between his own forces and those of Menelaus, sallying forth from Salamis. Demetrius took a calculated risk by leaving only a small force to impede Menelaus, and focusing the bulk of his forces against Ptolemy. The ensuing battle was a complete victory for Demetrius, who destroyed or captured much of Ptolemy's fleet and army. After the battle, Menelaus and his men surrendered, and the rest of Cyprus was captured by Demetrius. In the wake of this victory, Antigonus assumed the royal title that had been vacant since the murder of Alexander's underage son. This act influenced the other Diadochi to follow and imitate Antigonus and Demetrius. Soon after the battle, most Diadochi officially assumed the kingship.

The ballista (Latin, from Greek βαλλίστρα ballistra and that from βάλλω ballō, "throw"), plural ballistae or ballistas, sometimes called bolt thrower, was an ancient missile weapon that launched either bolts or stones at a distant target.

Developed from earlier Greek weapons, it relied upon different mechanics, using two levers with torsion springs instead of a tension prod (the bow part of a modern crossbow). The springs consisted of several loops of twisted skeins. Early versions projected heavy darts or spherical stone projectiles of various sizes for siege warfare. It developed into a smaller precision weapon, the scorpio, and possibly the polybolos.

The Shanhai Pass (simplified Chinese: 山海关; traditional Chinese: 山海關; pinyin: Shānhǎi Guān; lit. 'Mountain Sea Pass') is a major fortified gateway at the eastern end of the Great Wall of China and one of its most crucial fortifications, as the pass commands the narrowest choke point in the strategic Liaoxi Corridor, an elongated coastal plain between the Yan Mountains foothills and the Bohai Sea, which is the only easily traversable landway between North and Northeast China. It is located in present-day Shanhaiguan District, Qinhuangdao, Hebei province, on the east bank of the Shi River, with defensive walls stretching from the Yan Mountains all the way to the shores of the Liaodong Bay.

Throughout Chinese history, garrisons around the pass served as frontline defensive outposts against raids and incursions into the North China Plain by various non-Sinitic ethnic groups from the Northeast (also known as Manchuria since the 19th century), including the Dongyi, Donghu (Xianbei and Wuhuan), Khitan and Jurchen (Manchus). The current Shanhai Pass was built during the early Ming dynasty as the easternmost fortification of the Ming Great Wall, and was extensively reinforced after Yongle Emperor moved the capital from Nanjing to Beijing following the Jingnan campaign, making it the most important defensive barrier in all of China, as it shielded the heartland region around the imperial capital. The pass' strategic location dictated that without mounting a costly direct siege, the only way an invading army can get past the pass' defense was to circumvent it around the north through a few treacherously narrow mountain passes deep within the Yan Mountains, which would make it very difficult to maintain supply lines and thus any sizeable invasions. This defensive significance therefore earned the pass the famous nickname "Greatest Pass Under Heaven" (天下第一关).

A sortie (from the French word meaning exit, from Latin root surgere meaning to "rise up") is a deployment or dispatch of one military unit, be it an aircraft, ship, or troops, from a strongpoint. The term originated in siege warfare.

Hangu Pass or Hanguguan was a fortified gateway that commanded the strategic mountain pass between the Yellow River and Qinling Mountains, forming the main choke point on the only land corridor between the Central Plain and the Guanzhong region. The pass restricted access into the lower Wei River valleys, where the heartland of the state of Qin and the unified Qin dynasty were located, as well as the subsequent dynasties of Han, Sui and Tang.

The Hangu Pass lies on the south (right) bank of the Yellow River, 60 km (37 mi) downstream of its eastward bend out of the Ordos Loop. It was built by the state of Qin in 330 BC and had been the site of many sieges and field battles during the Warring States period and early imperial eras. Due to terrain changes from bank erosions and alluvial deposition of the Yellow River over the centuries, the Hangu Pass eventually fell to ruins after losing its defensive values to the newer Tong Pass to its west, which was built near the mouth of the Wei River in 196 AD by the warlord Cao Cao.