Fortification facts

Bourtange star fort, restored to 1750 situation, Groningen (province), Netherlands

Fortifications are military constructions and buildings designed for defense during war. People have constructed defensive works for many thousands of years, but the designs have become more and more complex. The term fortification comes from the Latin words fortis ("strong") and facere ("to make").

Many military installations are known as forts, although they are not always fortified. Larger forts may class as fortresses, smaller ones formerly often bore the name of fortalices. Some are castles. The word fortification can also mean the practice of improving an area's defense with defensive works. City walls are fortifications but not necessarily called fortresses.

The last great system of fortification to be built was the Atlantic Wall.



From very early history to modern times, walls have been a necessity for many cities. Uruk in ancient Sumer (Mesopotamia) is one of the world's oldest known walled cities. The Ancient Egyptians also built fortresses on the frontiers of the Nile Valley to protect against invaders from its neighbouring territories. Many of the fortifications of the ancient world were built with mud brick, leaving many no more than mounds of dirt for today's archaeologists.

Artists impression of the battlements at Buhen fortress in Egypt about 1800BC

The Assyrians deployed large labour forces to build new palaces, temples and defensive walls.

Some settlements in the Indus Valley Civilization were also fortified. By about 3500 B.C., hundreds of small farming villages dotted the Indus floodplain. Many of these settlements had fortifications and planned streets. The stone and mud brick houses of Kot Diji were clustered behind massive stone flood dykes and defensive walls, for neighbouring communities bickered constantly about the control of prime agricultural land. Mundigak (c. 2500 B.C.) in present day south-east Afghanistan has defensive walls and square bastions of sun dried bricks.

Pergamon Museum Berlin 2007110
Model of Ishtar Gate and part of the walls of Babylon built by Nebuchadnezzar

Babylon was one of the most famous cities of the ancient world, especially as a result of the building program of Nebuchadnezzar, who expanded the walls and built the Ishtar Gate.

Exceptions were few—notably, ancient Sparta and ancient Rome did not have walls for a long time, choosing to rely on their militaries for defence instead. Initially, these fortifications were simple constructions of wood and earth, which were later replaced by mixed constructions of stones piled on top of each other without mortar.

In Central Europe, the Celts built large fortified settlements known as oppida, whose walls seem partially influenced by those built in the Mediterranean. The fortifications were continuously being expanded and improved.

In ancient Greece, large stone walls had been built in Mycenaean Greece, such as the ancient site of Mycenae (famous for the huge stone blocks of its 'cyclopean' walls). In classical era Greece, the city of Athens built a long set of parallel stone walls called the Long Walls that reached their guarded seaport at Piraeus.

Large tempered earth (i.e. rammed earth) walls were built in ancient China since the Shang Dynasty (c. 1600-1050 BC), as the capital at ancient Ao had enormous walls built in this fashion (see siege for more info). Although stone walls were built in China during the Warring States (481-221 BC), mass conversion to stone architecture did not begin in earnest until the Tang Dynasty (618-907 AD).

In terms of China's longest and most impressive fortification, the Great Wall had been built since the Qin Dynasty (221-207 BC), although its present form was mostly an engineering feat and remodelling of the Ming Dynasty (1368-1644 AD). The large walls of Pingyao serve as one example. Likewise, the famous walls of the Forbidden City in Beijing were established in the early 15th century by the Yongle Emperor.

The Romans fortified their cities with massive, mortar-bound stone walls. The most famous of these are the largely extant Aurelian Walls of Rome and the Theodosian Walls of Constantinople, together with partial remains elsewhere. These are mostly city gates, like the Porta Nigra in Trier or Newport Arch in Lincoln.

Hadrian's Wall was built by the Roman Empire across the width of what is now northern England following a visit by Roman Emperor Hadrian (AD 76–138) in AD 122.


Genoese fortress in Sudak
Genoese fortress in Sudak, Ukraine
Ávila 24-8-2002
Ávila city walls, Spain

Roman forts and hill forts were the main antecedents of castles in Europe, which emerged in the 9th century in the Carolingian Empire.

Rumeli hisari
Rumelihisarı, İstanbul, Turkey

The Early Middle Ages saw the creation of some towns built around castles. These cities were only rarely protected by simple stone walls and more usually by a combination of both walls and ditches. From the 12th century AD hundreds of settlements of all sizes were founded all across Europe, which very often obtained the right of fortification soon afterwards.

Panorama of Malbork Castle, part 4
Castle of the Teutonic Order in Malbork: the world’s largest brick gothic castle, in Poland
Rio Miño y al fondo las murallas de ValenÇa
The fortified city of Valença, Portugal as seen from across the Minho River (Portugal's northern border with Spain)
Table of Fortification, Cyclopaedia, Volume 1
Table of Fortification, from the 1728 Cyclopaedia.
Krakow Fort31 20070413 1756
Austro-Hungarian Fort 31 Benedykt of Kraków fortress
Austro-Hungarian Fort I "Salis Soglio" of Przemyśl fortress
Ranikot Fort 07a
Ranikot Fort in Sindh, one of the largest forts in the world.

The founding of urban centres was an important means of territorial expansion and many cities, especially in eastern Europe, were founded precisely for this purpose during the period of Eastern Colonisation. These cities are easy to recognise due to their regular layout and large market spaces. The fortifications of these settlements were continuously improved to reflect the current level of military development.

During the Renaissance era, the Venetians raised great walls around cities threatened by the Ottoman empire. The finest examples are, among others, in Nicosia (Cyprus) and Chania (Crete), and they still stand, to this day.

Early Modern

Medieval-style fortifications were largely made obsolete by the arrival of cannons on the 14th century battlefield. Fortifications in the age of blackpowder evolved into much lower structures with greater use of ditches and earth ramparts that would absorb and disperse the energy of cannon fire. Walls exposed to direct cannon fire were very vulnerable, so were sunk into ditches fronted by earth slopes.

This placed a heavy emphasis on the geometry of the fortification to allow defensive cannonry interlocking fields of fire to cover all approaches to the lower and thus more vulnerable walls.

The evolution of this new style of fortification can be seen in transitional forts such as Sarzanello in North West Italy which was built between 1492 and 1502. Sarzanello consists of both crenallated walls with towers typical of the medieval period but also has a ravelin like angular gun platform screening one of the curtain walls which is protected from flanking fire from the towers of the main part of the fort.

Fortifications also extended in depth, with protected batteries for defensive cannonry, to allow them to engage attacking cannon to keep them at a distance and prevent them bearing directly on the vulnerable walls.

The result was star shaped fortifications with tier upon tier of hornworks and bastions, of which Bourtange illustrated to the right is an excellent example. There are also extensive fortifications from this era in the Nordic states and in Britain, the fortifications of Berwick-upon-Tweed and the harbour archipelago of Suomenlinna at Helsinki being fine examples.

19th Century

The arrival of explosive shells in the 19th century led to yet another stage in the evolution of fortification. Star forts of the cannon era did not fare well against the effects of high explosive and the intricate arrangements of bastions, flanking batteries and the carefully constructed lines of fire for the defending cannon could be rapidly disrupted by explosive shells.

Worse, the large open ditches surrounding forts of this type were an integral part of the defensive scheme, as was the covered way at the edge of the counter scarp. The ditch was extremely vulnerable to bombardment with explosive shells.

In response, military engineers evolved the polygonal style of fortification. The ditch became deep and vertically sided, cut directly into the native rock or soil, laid out as a series of straight lines creating the central fortified area that gives this style of fortification its name.

Wide enough to be an impassable barrier for attacking troops, but narrow enough to be a difficult target for enemy shellfire, the ditch was swept by fire from defensive blockhouses set in the ditch as well as firing positions cut into the outer face of the ditch itself.

The profile of the fort became very low indeed, surrounded outside the ditch by a gently sloping open area so as to eliminate possible cover for enemy forces, while the fort itself provided a minimal target for enemy fire. The entrypoint became a sunken gatehouse in the inner face of the ditch, reached by a curving ramp that gave access to the gate via a rolling bridge that could be withdrawn into the gatehouse.

Traditional fortification however continued to be applied by European armies engaged in warfare in colonies established in Africa against lightly armed attackers from amongst the indigenous population. A relatively small number of defenders in a fort impervious to iron-age weaponry could hold out against high odds, the only constraint being the supply of ammunition.

Much of the fort moved underground, with deep passages and tunnels to connect the blockhouses and firing points in the ditch to the fort proper, with magazines and machine rooms deep under the surface.

The guns however, were often mounted in open emplacements and protected only by a parapet - both in order to keep a lower profile and also because experience with guns in closed casemates had seen them put out of action by rubble as their own casemates were collapsed around them.

20th and 21st Centuries

Steel-and-concrete fortifications were common during the 19th and early 20th centuries. However the advances in modern warfare since World War I have made large-scale fortifications obsolete in most situations. Only underground bunkers are still able to provide some protection in modern wars. Many historical fortifications were demolished during the modern age, but a considerable number survive as popular tourist destinations and prominent local landmarks today.

Dragon's teeth—tank traps in the Eifel

The downfall of permanent fortifications had two causes:

  • The ever escalating power, speed, and reach of artillery and air power meant that almost any target that could be located could be destroyed, if sufficient force were massed against it. As such, the more resources a defender devoted to reinforcing a fortification, the more combat power that fortification justified being devoted to destroying it, if the fortification's destruction was demanded by an attacker's strategy. By 1950, nuclear weapons were capable of destroying entire cities, and produced dangerous radiation. This led to the creation of civilian nuclear air raid shelters. In the late 20th century, bunker busters were being used against bunkers.
  • The second weakness of permanent fortification was its very permanency. Because of this it was often easier to go around a fortification and, with the rise of mobile warfare in the beginning of World War II, this became a viable offensive choice. When a defensive line was too extensive to be entirely bypassed, massive offensive might could be massed against one part of the line allowing a breakthrough, after which the rest of the line could be bypassed. Such was the fate of the many defensive lines built before and during World War II, such as the Siegfried Line, the Stalin Line and the Atlantic Wall. Note that this was not the case of the Maginot Line, designed to force the Germans to pass through Belgium and that has fully achieved its political and strategic role.
Albania bunkers
Bunkers in Albania

Instead field fortification rose to dominate defensive action. Unlike the trench warfare which dominated World War I, these defences were more temporary in nature. This was an advantage because since it was less extensive it formed a less obvious target for enemy force to be directed against.

If sufficient power were massed against one point to penetrate it, the forces based there could be withdrawn and the line could be re-established relatively quickly. Instead of a supposedly impenetrable defensive line, such fortifications emphasized defence in depth, so that as defenders were forced to pull back or were overrun, the lines of defenders behind them could take over the defence.

Because the mobile offensives practised by both sides usually focused on avoiding the strongest points of a defensive line, these defences were usually relatively thin and spread along the length of a line. The defence was usually not equally strong throughout however.

The strength of the defensive line in an area varied according to how rapidly an attacking force could progress in the terrain that was being defended—both the terrain the defensive line was built on and the ground behind it that an attacker might hope to break out into. This was both for reasons of the strategic value of the ground, and its defensive value.

This was possible because while offensive tactics were focused on mobility, so were defensive tactics. The dug in defences consisted primarily of infantry and antitank guns. Defending tanks and tank destroyers would be concentrated in mobile "Fire Brigades" behind the defensive line. If a major offensive was launched against a point in the line, mobile reinforcements would be sent to reinforce that part of the line that was in danger of failing.

Thus the defensive line could be relatively thin because the bulk of the fighting power of the defenders was not concentrated in the line itself but rather in the mobile reserves. A notable exception to this rule was seen in the defensive lines at the Battle of Kursk during World War II, where German forces deliberately attacked into the strongest part of the Soviet defences seeking to crush them utterly.

The terrain that was being defended was of primary importance because open terrain that tanks could move over quickly made possible rapid advances into the defenders' rear areas that were very dangerous to the defenders. Thus such terrain had to be defended at all cost.

In addition, since in theory the defensive line only had to hold out long enough for mobile reserves to reinforce it, terrain that did not permit rapid advance could be held more weakly because the enemy's advance into it would be slower, giving the defenders more time to reinforce that point in the line. For example, the battle of the Hurtgen Forest in Germany during the closing stages of World War II is an excellent example of how impassable terrain could be used to the defenders' advantage.

After World War II, ICBMs capable of reaching much of the way around the world (and rockets capable of reaching the Moon and other nearby celestial bodies) were developed, and so speed became an essential characteristic of the strongest militaries and defenses. Missile silos were developed, so missiles could be fired from the middle of a country and hit cities and targets in another country, and airplanes (and air carriers) became major defenses and offensive weapons (leading to an expansion of the use of airports and airstrips as fortifications). Mobile defenses could be had underwater, too, in the form of nuclear submarines capable of firing missiles. Some bunkers in the mid to late 20th century came to be buried deep inside mountains and prominent rocks, such as Gibraltar and Cheyenne Mountain. On the ground itself, minefields have been used as hidden defences in modern warfare, often remaining long after the wars that have produced them have ended.

Demilitarized zones along borders are arguably another type of fortification, although a passive kind, providing a buffer between potentially hostile militaries.


US Navy 101211-N-6436W-098 Active duty and reserve component Seabees assigned to Naval Mobile Construction Battalions 40, 18 and 26 secure and fort
Engineers fill Hesco bastions at a forward operating base in Afghanistan


Forts in modern usage often refer to space set aside by governments for a permanent military facility; these often do not have any actual fortifications, and can have specializations (military barracks, administration, medical facilities, or intelligence). In the United States usage, forts specifically refer to Army fortifications; Marine Corps fortifications are referred to as camps.

However there are some modern fortifications that are referred to as forts. These are typically small semi permanent fortifications. In urban combat they are built by upgrading existing structures such as houses or public buildings. In field warfare they are often log, sandbag or gabion type construction.

Such forts are typically only used in low level conflict, e.g., counterinsurgency conflicts or very low level conventional conflicts, e.g., the Indonesia–Malaysia confrontation saw the use of log forts for use by forward platoons and companies. The reason for this is that static above ground forts can not survive modern direct or indirect fire weapons larger than mortars, RPGs and small arms.

North America

Fort Snelling 1844-Af000248
Fort Snelling on the confluence of the Mississippi and Minnesota Rivers, 1844. Image painted by John Caspar Wild (1804-1846).

In British North America, and subsequently in the frontiers of the United States, prior to the 20th century the term fort was increasingly used for any military base of operations regardless of how fortified it was. Military forts in the American Old West during the Indian Wars were often lightly fortified enclosures with log or adobe walls. In many areas the term fort was used to refer to any European or U.S. outpost, military, para-military, or civilian, that was located in an undeveloped region. Many of these outposts were simply trading posts or a combination of a trading post and an Army post.

Some famous U.S. military forts included Fort Laramie and Fort Bridger on the Emigrant Trail and Bent's Fort on the Arkansas River.

Related pages


Fortification Facts for Kids. Kiddle Encyclopedia.