Impromptu Fortress

Leave it to the French to turn a public avenue into a warzone.

We're all familiar with the archetypical castle: Walls, gates, towers, moats. There are plenty of ways of designing a dedicated structure to defend and hold a position, but they share some fundamental drawbacks: They're expensive to build, tricky to maintain, difficult to conceal, and, most obviously, impossible to move around as the situation calls for it. Many forts would find themselves encircled, bypassed, or abandoned because of it.

This is why many characters, real and fictional alike, may be tempted to simply turn the next best place into a stronghold: right here, right now, and for the foreseeable future. It can be done in a natural landmark — be it a hill, a river crossing, or a forest - but one can just as easily fortify a suitable building intended to serve a non-tactical purpose — like a factory, a church, or even a simple farmstead or public square.

Such structures are, naturally, makeshift in nature and borne of an immediate necessity to deter a much stronger enemy. Even if it may not be ideally suited to the desired purpose, it will generally make do in a pinch and is almost certain to cause most would-be besiegers at least an undue amount of headache.

This trope is a natural staple of Zombie Apocalypse, Survival Horror, and apocalyptic fiction in general, what with the abundance of decaying infrastructure in regions teeming with monsters or marauders. When fighting against The Empire or another sapient, organised force, it generally also falls into the realm of La Résistance, wielding various improvised weapons.

Compare Improvised Imprisonment. See also Garrisonable Structures for this trope's video game interpretation.

Weaponized Landmark is its Sister Trope. Whereas this is a landmark serving as a defense against hostile attack, the Weaponised Landmark is used to strike at adversaries.

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Examples:

Fan Works

• The Dark Lords of Nerima: When the Nerima Wrecking Crew find themselves in conflict with the Sailor Senshi and Dark Kingdom, and Ranma comes up with his crazy plan of posing as interdimensional conquerors, they decide to hole up in Furinken High School as their "evil lair" since they know the layout and can use the home turf advantage.
• Saruman of Many Devices: The Army of the White Hand is thoroughly trained and organised. When on the move, its companies are able to set up a temporary palisade around their nightly camp within twenty minutes; nothing compared to a city wall, but enough to blunt the effect of a cavalry charge.

Films — Animated

• The Hunchback of Notre Dame: The Catholic priests barricade the doors to the cathedral to prevent Judge Frollo's mooks from violating the sanctity of the church. Quasimodo, Phoebus, and Esmeralda have taken sanctuary in its belltowers and can see the hostile forces attempt to batter through the main doors. Gargoyle adornments that can "vomit" hot oil, plus Parisians upset that the "heart" of Paris is besieged contribute to keeping the mooks out, though Frollo himself manages to find a way inside.
• Treasure Planet: Jim Hawkins is scouting the planet for a defensible position when he encounters the nutty robot B.E.N. The robot takes him to his home, which is an egg-shaped promontory with a single entrance overlooking a wide-level terrain. Since the entire planet is one huge portal generator, this cannot be a military post; rather, an access hatch in its floor that leads to the vast mechanized interior suggests a service bay. Jim reports back with this discovery of an essentially armored bubble with a perfect field of fire, where Doctor Doppler, Captain Amelia, and Morph can make their stand against Silver's pirate band.

Films — Live-Action

• 28 Days Later: Father and daughter duo Frank and Hannah are holed up at the top of a block of flats, barricading the stairs with shopping carts, and Frank has procured a set of police riot gear to fight the infected off.
• 71: Into the Fire, which is based on a Real Life incident from the Korean Civil War where the P'ohang-dong Girls school is converted into a military checkpoint, with the titular seventy one South Korean teen conscripts tasked with defending it from a North Korean attack.
• Dawn of the Dead:
  • The original has one of the most iconic ever to be filmed: a shopping mall, fortified with the help of built-in alarms and burglar-proof glass, combined with trucks blocking the entrances, so the zombies can't gain any momentum and thus access. Zombies. On top of that, Peter and Stephen built a fake wall to hide the existence of the service corridor leading to the part of the mall the group took over for their apartment, but the wall is just a wooden frame and some painted plywood.
  • Downplayed in the sequel. The shopping mall becomes the fortress for the main characters, but they put in minimal effort to actually bolster its "natural defenses". It bites them in the ass twice, first when there is a power shortage and then when they are forced to leave the place in a hurry - in both cases they would prevent themselves a lot of trouble by securing the place properly.
• Dredd places two Mega-City One judges trying to investigate a death at a large housing block, which has a new gang selling Slo-mo fortified in the top floors.
• In The Eagle Has Landed, the Luftwaffe commandos take over a scenic English village, transforming the church into their main base and the adjacent pub and water mill into outposts.
• The climax of L.A. Confidential has Exley and White ambushed inside a run-down motel complex. Thinking quickly, they retreat into one of the rooms and punch firing holes into the walls and floors, transforming it into essentially a blockhouse from where they can lay down fire on the attackers in all directions.
• Letters from Iwo Jima is a Dramatization of the World War II assault by the US Marines against the island of Iwo Jima, based upon letters written by the Japanese defenders that served as an Apocalyptic Log. Mount Suribachi in the southwestern part of the island already had a system of caves, and these were expanded into a tunnel network like a human-sized ant colony. From there, Japanese soldiers hunkered down while the American Navy pounded the island with thousands of shells. The tunnels held, but the bigger problems of food shortages, no sanitary sewers, and dysentery proved to be as formidable as the American assault force.
• The Raid is about a police tactical team trying to infiltrate a derelict apartment building that has been made into a fortress by a gang of criminals.
• Shaun of the Dead: Shaun is convinced that The Winchester pub is the best place to hide out during the outbreak.
• The Siege of Jadotville: Truth in Television. The Irish UN peacekeepers set up camp in a derelict compound located in the middle of a barren plain. It is only thanks to Commandant Pat Quinlan's know-how of siegecraft that the compound is transformed into a deadly bulwark that manages — at least for a time — to withstand a massive assault of a superior number of better-equipped mercenaries supported by artillery and aircraft.
• Zulu, taking place during the 1879 Battle of Rorke's Drift, focuses on a small company's worth of British soldiers turn a modest Swedish mission house-turned-military hospital into a well-fortified outpost that successfully faced off against an assault of approximately 4000 Zulu warriors.

Literature

• In Discworld's Night Watch, in an homage/parody of Les Misérables, the city is in chaos due to military action against La Résistance. The city (both regular citizens and members of La Résistance) have put up defensive barricades to keep out soldiers. It comes to Watchman Fred Colon's attention that, despite the military propaganda to the contrary, the violent chaos seems to be outside the barricades, rather than inside. When his superior, Sergent Sam Vimes, returns, Vimes finds that his men have extended and fortified the barricades to engulf most of the city.
  Colon: Supposing the area behind the barricades was bigger than the area in front of the barricades, right? Like, sort of, it had more people in it and more of the city, if you follow me... That'd mean in a manner of speaking we are now in front of the barricades, am I right? Then, as it were, it's not like we're rebellin', is it? 'Cos there's more of us, so the majority can't rebel, it stands to reason. So that makes us the good guys. Obviously we've been the good guys all along, but now it'd be kind of official, right? Like, mathematical? So, we thought we'd push on to Short Street and then we could nip down into Dimwell and up the other side of the river...
  Colon: Are we going to get into trouble for this, Sarge?
  Colon: You're looking at me in a funny way, Sarge.
  Colon: Sorry, Sarge.
• The Defence of Duffer's Drift and its various remakes commit themselves entirely to this trope. In the first iteration alone, advised places to fortify range from river crossings to hillside villages to riverbeds — with varying degrees of success.
• In Roderick Thorp's Nothing Lasts Forever (the source novel for Die Hard), the protagonist, John Leland, realizes that with the elevators locked out, and the security gates preventing access to the building's stairwells, the Klaxon Oil corporation's headquarters building becomes almost as secure as a medieval castle. Nakatomi Tower becomes this in the film.
• In I Am Legend, Neville turned his own house into his castle, in a very literal way. It's implied early on that it just happened on its own as a completely improvised boarding up, but when the story opens, he already put extra effort to it and as time goes on, the defenses get more and more elaborate. Every film adaptation had it included in an increasingly complex effort to fortify otherwise civilian buildings.
• The Riftwar Cycle offers an interesting variant: in Shadow of a Dark Queen, the mercenaries led by Calis and Robert de Loungville routinely build their camps as miniature forts. Truth in Television: this was a standard tactic of Roman legions on the march during Rome's campaigns of conquest.
• World War Z: "The Battle of Five Colleges" saw students from different college campuses in Los Angeles using the university buildings as forts and a handful of rifles from their ROTC offices as weapons to successfully delay the zombie horde from spreading further in the city.

Live-Action TV

• Dad's Army: In "The Battle Of Godfrey's Cottage", due to a misunderstanding, Captain Mainwaring is left believing the invasion has begun, and that the majority of the platoon are out of Warmington-On-Sea. Having only Jones and Frazer (as well as Godfrey as he later discovers) to hand and realising they have no hope of repelling any invasion force on the beaches, they resort to setting up an improvised base at Godfrey's cottage due to it being in a key strategic point on the main crossroads out of town, hoping they will be able to at least hold the invading Nazi's off long enough for General HQ to organise a proper counterattack (and them all openly acknowledging they will certainly die in the process). This leads to them setting up the Lewis gun out the living room's window, and resorting to using Godfrey's pillows filled with crockery as makeshift sandbags.
• Doctor Who: In "Nightmare in Silver", needing a place to set up a defensive position against the Cybermen in Hedgewick's World of Wonders, Clara selects Nanny Longshoes comedic castle, as whilst it's only an amusement park attraction it's still a full-sized castle with a moat, and thus their best option.
• Firefly: "Heart of Gold" sees Mal and his crew persuaded to turn the brothel they've been hired to protect into a fortress against local aristocrat Rance Burgess, who has deliberately impregnated one of the girls and is coming to retrieve "his" child by force. They distribute what spare weapons they have, Wash and Zoe bury a cable under the entrance that can be raised to knock attackers off their steeds, Shepherd Book nails boards across the upper floor windows to create concealed firing positions, and Kaylee upgrades the well pump for use in fighting fires.

Music

• Sabaton: Rorke's Drift describes how the support column to a British army wiped out by the Zulus at the Battle of Isandlhwana swiftly worked to build barricades of boxes around their position at a Christian mission against the oncoming African army.

Tabletop Games

• BattleTech: In urban warfare, infantry, vehicles, and sometimes even mechs can enter building hexes and shoot out of them to hit enemies while the building provides some protection. This is risky, however, because the building itself can also be shot at and if it takes enough damage it will collapse on whatever units are inside it.
• In Red Markets most enclaves in the zombie-infested Loss are pre-Collapse buildings hastily converted into improvised fortresses. Notable examples include a mall with a wall made of wrecked cars, a fitness club powered by zombies on treadmills, a hunting and sports superstore controlled by feuding groups of anarcho-capitalists, and an entire Taker group that specializes in converting retirement homes into new enclaves.

Video Games

• Batman: Arkham City: With whole sections of Gotham hastily walled off to make a massive prison complex, multiple supervillains have taken advantage of this to convert the buildings into their new bases of operations:
  • The Joker has taken over the old Sionis Steel Mill (which he stole from Black Mask), taking advantage of the still functioning machinery and forge to build up his defences and set a series of traps.
  • Before the events of the game, the Penguin had already converted his club, the Iceberg Lounge into a fortress, when the eviction order came through both the Police and Strange's Tyger Guards failed to get him out, thus forcing them to build around him. Afterwards, Cobblepot expanded to also incorporate the nearby Cyrus Pinkney Institute for Natural History into his base, taking advantage of the Museum's state-of-the-art security system and installing all his own defences.
  • At the start of the game Two-Face is in the process of converting the Solomon Wayne Court House into his base of operations. Following being defeated and breaking free in the DLC he takes advantage of the Penguin's defeat, to take over the Museum and tries to turn this into his new base, before being defeated by Catwoman.
  • Having lost his steel mill to the Joker, Black Mask was forced to resort to turning the Sionis Meat Packaging facility into his new base. Following the aftermath of Protocol Ten and the Joker's demise, he attempted to take advantage of the chaos to take over, but was foiled by Robin.
• Batman: Rise of Sin Tzu: Downplayed. In the final chapter, it's revealed that the Sin Tzu has turned Arkham Asylum into his base as "there is little difference between a fortress and a prison." However, Commissioner Gordon notes that the asylum defences were built specifically not just to keep the inmates inside, but also to stop anyone from breaking them out, meaning the GCPD can't storm to retake it and Batman has to infiltrate through the sewers.
• Brothers in Arms: Since fighting often takes place often in French and Dutch towns, villages, and cities, many French and Dutch churches, mansions, farmhouses, and even windmills are turned into vital defensive positions or outposts that must be defended from German counterattacks. The most notable of these is the Cathedral in the middle of Carentan, which Baker and his squad are forced to hold against a large counteroffensive by SS mechanized infantry and their tank support. Baker ends up using the bell tower and upper floors as a vantage point for his Sniper Rifle, while Hartsock, Corrion, and the rest of the squad use the church's outer fences as cover.
• Call of Duty:
  • Call of Duty
    • "Pavlov's House" has Sgt. Alexei Ivanovich Voronin reinforce Sgt. Pavlov's squad just outside the titular apartment block, which has since been turned into a makeshift outpost and defensive position. Following a successful attack that wipes out the German forces holding the building, Voronin, Pavlov, and other Soviet soldiers must Hold the Line against a massive German counterattack.
    • The "Berlin" level of the Soviet campaign features the Reichstag, the German Parliament building, as the final German stronghold in Berlin, which is defended by a ragtag unit of Wehrmacht and Waffen-SS soldiers. While the outside area is mostly abandoned, the Germans have fortified the interior and exterior of the building with machine gun nests. In addition, they've also posted a number of immobilized tanks and anti-tank guns around the building in an attempt to hold back the Soviet tidal wave.
  • Call of Duty 2 has several examples in all three campaigns.
    • The Soviet campaign has several bombed-out apartment blocks, the Stalingrad city hall, and, Most notably, Railroad Station Number 1, turned by both the Germans and Soviets into makeshift defensive positions/supply depots/headquarters, with constant close-quarters fighting and subsequent counteroffensives to capture and hold these positions for good. Ultimately, the Soviets manage to hold all of these positions by the end of the campaign and force the Germans back.
    • The British campaign has several North African and French villages turned into defensive positions/headquarters/outposts by both the Germans and British. In addition to these, the Germans have also managed to fortify sections of the Egyptian and Libyan deserts against British tank and infantry attacks, laying minefields, Anti-Vehicle guns, and machine gun nests in wide areas in between hills and dunes.
    • The American campaign has a French hamlet turned by the Germans into a forward headquarters and base for their artillery. During the events of "The Silo", Dog Company of the 2nd Ranger Battalion are tasked with capturing the entire village, and then later holding it against a massive German infantry attack. Later, during the final level, the Germans turn the riverside town of Wallendar into an improvised fortress, placing artillery guns in every block, machine gun emplacements covering every street, and Anti-Infantry and Anti-Vehicle obstacles covering every crossroad.
  • Call of Duty: World at War: The Reichstag, the German Parliament building, is turned by Wehrmacht and Waffen-SS soldiers into their final stronghold in the center of Berlin, overlooking the entirety of the city center. To defend these ruins, they've placed several Anti-Vehicle guns around the outside, fortified several buildings near the Reichstag itself into makeshift bunkers, and, on the inside, created several impromptu pillboxes and fortifications made from a mix of construction materials and sandbags.
• In Cepheus Protocol, the player is encouraged to make use of existing civilian structures to build anti-zombie exclusion zones, death funnels, sniper nests, or similar. Notable such areas include sports stadiums, fairgrounds, destroyable bridges, sprawling mansions, nature parks, and high-rise buildings (as well as some slightly more traditional defensive structures like fenced military bases).
• In Dead to Rights: Retribution, the Grant City Anti-Crime Unit set up two separate bases to amass all their forces and technology in anticipation of their assimilation over Grant City, one in the ruins of a sports stadium that was abandoned during construction, the other in an abandoned hospital on the neighboring Danvers Island. They also end up taking over the GCPD Precinct late in the game, and it's up to Jack Slate to take GAC down in all of them.
• The Division and The Division 2 are both set in the immediate aftermath of a social collapse, leading to various factions grabbing all and any buildings within a single city to turn into living spaces and fortresses. Player characters set up headquarters within the James A. Farley Building in New York, or the White House in Washington D.C., and get to see how enemy factions have coopted the existing infrastructure for their own ends, whether it's a TV studio repurposed as a broadcast center, the Air & Space Museum turned into a missile factory, or Capitol Building becoming a warlord's castle (with a salvaged A-10 Warhog's gatling gun set up at the front door).
• Fallout:
  • Fallout:
    • Downplayed with Brotherhood of Steel's bunker. It used to be a small military depo that got gradually expanded over the years into its current form, but by the time the Vault Dweller arrives there, it's hardly improvised.
  • Fallout 3:
    • The Jefferson Memorial has been co-opted as the site of Project Purity, aiming to provide the Capital Wasteland with clean water. Unfortunately, it was overrun by Super Mutants who set up defenses, then retaken by the Lone Wanderer and their father. It again gets taken, this time by the Enclave, who naturally fortify it, before the Lone Wanderer brings the Brotherhood of Steel to retake it once again. With the Broken Steel DLC, it is revealed that the Brotherhood has turned it into a base and are the ones distributing the purified water.
    • The Brotherhood's home base, the Citadel, is built into the ruins of the Pentagon which they've heavily fortified.
    • Rivet City is a pre-war dry-docked aircraft carrier that has been fortified and turned into the largest settlement in the Capital Wasteland.
  • In New Vegas there's also the Hoover Dam (a fortified strategic river crossing), and for a lesser one, the Las Vegas airport (repurposed into a military base).
  • Fallout 4:
    • "The Castle", the traditional headquarters of the Commonwealth Minutemen, is an interesting case in that it was originally a military fortress, but one initially built centuries before the game takes place to defend against very different types of enemies. A pre-war historical site, the Minutemen co-opted, repaired, and reinforced it, adding a radio tower to quickly communicate across the Commonwealth. Unfortunately, 47 years before the events of the game, it was sacked by a Mirelurk Queen and became overrun with her progeny. The Sole Survivor can help to reestablish the Minutemen and retake the Castle.
    • After the Brotherhood of Steel arrives in the Commonwealth via Dynamic Entry in their zeppelin battleship, the Prydwen, they fly it to the Boston Airport which they then fortify as their base of operations in the area.
    • Numerous other smaller factions and settlements have fortified various Boston landmarks to use as homes/bases. For example, Bunker Hill is a walled-off trading settlement set up around the eponymous landmark, a group of robots have fortified the U.S.S. Constitution (including outfitting it with rocket thrusters), the Railroad has set up their base beneath the historical Old North Church, and many more.
    • Thanks to the game's base-building mechanics, it's possible to turn anywhere you can build in the Commonwealth into this by setting up barricades, walls, and automatic turrets to repel attackers.
• The early stages of each and every war in Foxhole are about advancing as much as possible and then dig-in in the eponymous foxholes, while also securing civilian buildings in the area, as they are easier to hold and defend and don't have to be built first. Actual field fortifications come a few days later. And every time the frontline shifts, new impromptu fortifications must be set up. while any urban area turns into a Stalingrad-tier meat-grinder, with people fighting over every threshold.
• Hell Let Loose: On the Stalingrad map, several buildings, which range from small shanties to large apartment blocks like Pavlov's House, are located within or near the various Capture Points on the map. Because of their strategic location, these buildings are often fortified by the forces of either side and must either be held or taken out in order for one side to fully control the Point.
• Commonplace within the The Last Stand franchise. The original game had a random farmhouse fortified with fuel barrels, boards and cinder blocks, while the sequel enforced this trope even more, as the group of survivors was constantly moving around and switching their locations, forcing them to fortify the weirdest of places (including a church, a car workshop, or a random boiler room). The MMO put players in a randomly assigned building within Union City, with half of the gameplay being endless sieges and tricks on how to deal with them with improptu barricades to not get overrun.
• Mass Effect 2
  • Mordin's mission has Shepard assaulting the base of Clan Weyrloc, which is an old hospital. This may as well, be an actual fortress, however, as krogan hospitals have to be sturdy enough to withstand krogan who are going into blood rage.
  • The mission to recruit Archangel leads to his base, an apartment with a bridge directly in front of it which provides the only access, giving him a clear line of fire at anyone trying to reach his base. This enables him to hold off entire waves of Mooks by himself, but it also keeps his attention focused there, so if anyone manages to flank him he'd be at a significant disadvantage. Until Shepard shows up, that is.
• Medal of Honor: Underground: "Last Rites at Monte Cassino" features the Abbey at Monte Cassino, a Catholic monastery located atop the titular mountain turned by the German Army into a mountaintop fortress, complete with roadblocks, machine gun nests, and miles worth of obstacles. Manon Batiste is tasked with liberating several captured American airmen being held in its basement section, as well as destroying the German armor, ammunition, and fuel supplies located within and near the monastery.
• This is part of the core gameplay of Rainbow Six Siege, as the defending team has a short amount of time each round to hastily fortify the building with steel walls, bulltproof doors, hidden cameras, shields, etc.
• In Red Alert 2 and Red Alert 3, infantry can enter civilian buildings and fortify them.
• Star Wars: The Old Republic: Knights of the Eternal Throne Chapter I: "Wrath and Ruin" has the Player Character and The Alliance forced to Hold the Line with the Voss commandos inside the Tower of Prophecy while Vaylin subjects the city of Voss-Ka to Orbital Bombardment and sends wave after wave of Mecha-Mooks to wipe you out.
• State of Decay: Every single safehouse, along with NPC enclaves, is a completely improvised fortification made out of regular places. You start with the Church of the Ascension in Spencer's Mill, which has the advantage of being walled (but the wall isn't too high nor impenetrable) and kinda on the side of the town, making it safer due to the distance, but the game outright demands to find a new spot to move and fortify, as the church is at the capacity limit and not really that safe. Choices include: other houses with walls around them, truck depos, fair grounds, secluded farms and even a Mexican restaurant. All of those places are nowhere truly safe and secured, not to mention resembling an actual fortress (well, The Alamo restaurant does, but that's merely the appearance), but they are the closest things in the whole Trumbull Valley. On top of that, every single house can (and some must be) fortified on a fly, by boarding the windows and calling backup via radio.
• It's mentioned in the backstory of several maps in Unreal Tournament III that the Necris don't construct buildings, but they infect already existing buildings, turning them into operational bases. This is seen in several of the maps such as WAR-Avalanche (whose buildings are powered by Nanotubes falling from their dimension), CTF-FacingWorlds, vCTF-Corruption and WAR-Islander_Necris (where, in all cases, the Blue base is shown with nanotubes spreading all the way).
• Valheim: A great many buildings built by previous occupants of Valheim still dot the landscape (villages, towers, keeps...), and players are encouraged to use them as bases or at least base camps, especially since many of them still have multiple floors which enemies can't climb. The main difficulty is that they tend to already be occupied with hostiles.

Real Life

• Wagon forts were historically used to improvise fortifications in areas that offered zero natural protection. Their complexity ranged from a completely improvised "circle of wagons" in the prairie to purpose-built carts with one of the sides reinforces into a battlement and that could be chained together and set up as an actual, mobile stockade of sorts. Probably the most famous uses were the Taborites during the Hussite Wars (giving the name of such a contraption to Central and Easter Europe), followed by Cossacks tabor and Afrikaaner lager. Sometimes those were set up in fully stationary positions, with earth embankments and gabions - particularly during sieges against actual, purpose-built fortifications.
• John Brown's doomed 1859 raid on Harper's Ferry ended with Brown and his remaining compatriots barricading themselves in the local fire station's engine house, where they would block the gates and punch firing holes into the walls and doors. Ultimately, a detachment of US Marines managed to punch a sizable hole of their own and storm the building.
• The Haun's Mill massacre during the 1838 Mormon Wars was a tragic example when the defenders used a blacksmith shop as their refuge. Unfortunately for them, while the thick logs of the walls were certainly bulletproof, there were gaps between the logs large enough to fire a rifle through, turning the building into a deathtrap.
• A predominant tactic in Urban Warfare throughout human history:
  • A famous example, set during the gruelling siege of Stalingrad was Pavlov's House, a three-sided apartment building fortified by Red Army soldiers, which successfully held against German attacks for 60 days, despite being shelled and breached multiple times, even culminating in room-to-room fighting.
  • The 1934 siege of Vienna's Karl-Marx-Hof — to this day the longest continuous housing complex in the world — is a weaker example of this trope. While on the one hand, it was constructed to resemble a castle at least superficially, it quickly turned out to be a lousy place to make a last stand. After socialist militiamen barricaded themselves inside the massive complex, the Austrian Bundesheer bombarded it with blank ammunition, nevertheless causing notable damage to the building's substance. The defenders surrendered before any casualties could be sustained.
• Subverted with European fortress churches, which typically started off as ordinary churches but were, over decades or centuries, increasingly fortified to act as small but proper castles during times of war and upheaval.
• The Eighth Power Station in what is today the town of Kirovsk served as an impromptu fortress for the Nazi troops on the Leningrad Front until mid-1944.
• Any catacomb or civilian Tunnel Network can, once extensive or deep enough, become nigh-impenetrable to outside enemy threats. Particularly famous cases are the Paris and Odessa catacombs, which saw extensive wartime use as air raid shelters, smuggling routes, and, most vitally, resistance strongholds against German occupation.
• During the American Civil War, both Union and Confederate troops became very good at building makeshift forts and defensive works. In 1864 and early 1865, the Confederates got so good at this that some late-Civil-War battlefields resemble the trenchworks that figured heavily in the First World War half a century later.

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