The 25 strongest castles in Europe

The largest castle on earth by land area, its High, Middle and Lower castles enclose some twenty-one hectares behind rings of brick wall and dry moat, roughly four times the footprint of Windsor, and on its completion in 1406 it was the largest brick fortress in the world. The Teutonic Knights raised it as their crusading capital, supplied by river and defended in depth, so that to break in an attacker had to storm three linked castles one after another.

It was never taken by storm. When the armies of Poland and Lithuania besieged it in the summer of 1410, fresh from their victory at Grunwald, the commander Heinrich von Plauen held out until the siege collapsed. Malbork left the Order's hands only in 1457, and then not to an enemy but to a bill, its own unpaid mercenaries sold the fortress to the Polish crown.

Richard the Lionheart threw up Gaillard in barely two years, from 1196 to 1198, as the most advanced castle of its age, perched ninety metres above a loop of the Seine to bar the French road to Rouen. Its stacked baileys and one of the earliest uses of machicolations in Europe made it the model fortress of its generation, Richard is said to have looked on it and called it his 'fair daughter.'

It fell only once, and it took the King of France to do it. Philip II sat before the walls from September 1203 to March 1204; his men undermined the outer bailey, then slipped into the middle ward by climbing up a latrine chute into the chapel, and finally forced the inner gate. The garrison surrendered, Normandy fell with the castle, and the ruin still crowns the cliff above Les Andelys today.

The 'Key of England,' Dover is the great fortress of the Channel coast, a mighty square keep raised by Henry II inside two concentric rings of wall and mural towers, standing on the white cliffs above the shortest crossing to France. It was the hinge on which control of the whole south-east could turn.

No besieging army ever took it. In 1216–17, during the war between King John's party and the future Louis VIII of France, French miners brought down part of the north gatehouse, but Hubert de Burgh's garrison plugged the breach and held, and the wrecked gate was rebuilt as an underground system of defensive tunnels. Dover changed hands only once, in 1642, and then by stealth: a handful of men scaled the cliffs at night and seized it without a fight.

The crown of Edward I's 'iron ring' of Welsh castles, Caernarfon was begun in 1283 to overawe a conquered people. Its banded, many-sided towers and the twin-towered King's Gate, with its drawbridges, portcullises and murder-holes, make it, in one historian's words, the most striking demonstration of the strength of medieval fortification in Britain.

It was taken once, in 1294, when Madog ap Llywelyn's revolt caught it still half-built and defended by little more than a ditch and a timber barricade; the English retook and finished it the next year. Once complete it proved its worth, a garrison of barely thirty men holding it through Owain Glyndŵr's sieges of 1401 to 1404. It yielded at last only to Parliament in 1646, and by surrender rather than storm.

Edinburgh Castle sits on the plug of an extinct volcano, sheer cliffs falling away some eighty metres on three sides, with only the eastern 'tail', the Royal Mile, open to attack. Research published in 2014 counted twenty-six sieges across its eleven centuries, a claim to being the most besieged place in Britain and one of the most attacked in the world.

That record cut both ways: it fell many times, but almost always by daring or treachery rather than by breaching its walls. In 1314 thirty of Robert the Bruce's men scaled the north cliff in darkness and retook it; in 1341 Scots disguised as merchants jammed a cart in the gateway to hold it open. Only in the Lang Siege of 1573 did brute force win, when English cannon fired some three thousand rounds and brought David's Tower crashing down.

One of the largest fully preserved medieval fortresses in Europe, Hohensalzburg crowns the Festungsberg above Salzburg, its ring walls and towers reinforced over the centuries with bastions raised against the Ottoman threat. The prince-archbishops built it to be unassailable, and for the most part it never even had to fight.

In more than nine hundred years it was never taken by force. Its one real test came in the Peasants' War of 1525, when miners and townsfolk failed to break in, the siege that gave rise to the tale of the archbishop parading his last ox, freshly repainted each day, to fake endless supplies. The fortress finally opened its gates in 1800, but to a bloodless surrender to Napoleon's advancing French, never to an assault.

Königstein stands on a table of sandstone rising some 240 metres above the Elbe, its nine-and-a-half-hectare summit ringed by nearly two kilometres of wall above sheer rock faces, with a 152-metre well, the deepest in Saxony, to see it through any siege. It was less a castle than a mountain with a garrison on top.

It was never conquered. So sure was its reputation that Saxony trusted it with the state treasury and its most dangerous prisoners, and armies preferred to avoid it rather than test it, in the Seven Years' War the Elector could only watch from its heights as his army was forced to surrender on the plain below. The one man ever to breach its defences was a chimney-sweep who free-climbed the cliff for a dare in 1848.

Stirling guards the lowest crossing of the River Forth from a volcanic crag walled by cliffs on three sides, the strategic clasp between the Scottish Lowlands and Highlands, and for that reason one of the most fought-over strongholds in Britain, with at least eight sieges to its name.

It changed hands again and again through the Wars of Independence, more often starved or bargained into surrender than stormed. Its most famous siege came in 1304, when Edward I ringed it with seventeen engines and built a giant trebuchet called the 'Warwolf'; the garrison offered to give up, but Edward made them wait inside until he had smashed the gatehouse with a shot from his new machine.

Conwy's eight great drum towers and two barbicans rise straight from a rock above the estuary, guarded on the landward side by walls that could be resupplied from the sea, one of the finest surviving works of medieval military architecture in Europe, built for Edward I in just four years by James of St George.

For all its strength it was twice taken. On Good Friday 1401, while most of the garrison was at church in the town, a band of some forty men loyal to Owain Glyndŵr talked their way in, killed the watch and held the castle for three months. It fell again in 1646, to a proper siege in the Civil War, but back in 1294 the great fortress had done its job, sheltering Edward himself through a winter until relief arrived by sea.

At more than a kilometre from end to end, Burghausen is the longest castle in the world, a record confirmed by Guinness. It is strung along a narrow ridge with the Salzach river on one side and a lake on the other, a chain of six courtyards each sealed behind its own fortified gate, so that an attacker who forced one still faced five more.

Under Duke Georg of Bavaria around 1500 it was reckoned the strongest fortress in the region, and its layered gates were never breached in a set-piece assault; in the Thirty Years' War it was secure enough to hold a captured Swedish general for seven years. Its long defensive career ended not in battle but by decree, when Napoleon declared the old fortress militarily obsolete in 1809.

The Castle of Cardona commands its town and the strange salt mountain below it from a steep hill that made close approach treacherous, its medieval core stiffened in the eighteenth century with bastions and casemates for artillery. Catalans called it impregnable, and its history earned the name.

It was never taken by force. In 1711, during the War of the Spanish Succession, a Bourbon army some fifteen thousand strong bombarded it for over a month before a relief column drove them off. When Cardona finally lowered its flag in September 1714 it was the last Catalan stronghold still holding out, and even then it surrendered by negotiated terms, a week after Barcelona had fallen, rather than to a storming.

Coucy was crowned by the greatest keep ever built in medieval Europe, a cylinder some thirty-five metres across and fifty-five metres tall, its walls up to seven and a half metres thick, raised in the 1220s by a lord who boasted he was neither king nor prince but simply the Sire de Coucy. Four vast corner towers guarded the walls around it.

Its walls were never stormed; when it fell in 1411 after a three-month siege, it was hunger, not the enemy, that opened the gates. Even Cardinal Mazarin's engineers failed to bring the great keep down when they tried to slight it in 1652. It stood almost intact until 1917, when the retreating German army packed it with some twenty-eight tonnes of explosive and blew it apart, an act France condemned as a monument to barbarity.

Acrocorinth is the mightiest of the Greek acropolis-fortresses, a monolith rising close to 575 metres above ancient Corinth to command the isthmus into the Peloponnese. Three successive lines of wall climb the rock, and a spring high inside the walls meant the garrison need never run dry, a fortress built to outlast any siege.

Byzantines, Franks, Venetians and Ottomans all held it in turn, and its strength shows in how it usually changed hands: by long blockade and starvation, or by treaty, rather than by assault. Its Greek defender Leo Sgouros held out here for years against the crusaders before, in 1208, he is said to have galloped his horse off the summit rather than surrender; his garrison fought on for two years more.

Marksburg guards the Rhine from a steep cone above Braubach, a compact fortress of keep, hall and triangular curtain wall later bristling with gun bastions. It is the exception among the river's castles, of the forty or so strongholds strung between Bingen and Koblenz, it is the only one never destroyed and the only one never left to fall into ruin.

No great siege ever tested it; its survival is the story of a fortress so well sited and so well kept that it was never worth the cost of taking. The only serious harm in eight centuries came late and from a distance, when American guns firing across the Rhine in March 1945 damaged it, and even then it was repaired, and stands whole today.

The Sforza Castle grew from Francesco Sforza's fifteenth-century rebuilding into one of the largest citadels in Europe, its walls up to seven metres thick and, under Spanish rule, wrapped in some three kilometres of star-shaped bastions manned by thousands of troops. Its defences drew on the finest engineers of the Renaissance, Leonardo da Vinci among those who worked on them.

Yet for all its scale, Milan's fortress was fought over and fell repeatedly through the Italian Wars. Its most decisive loss came in 1515: after his victory at Marignano, Francis I of France set his sappers to mine the foundations, and the garrison capitulated. Six years later disaster struck from within, when its great Filarete tower, used as a powder store, blew up and killed scores.

Beaumaris is the textbook 'perfect' concentric castle, a high inner ward of six towers and thick walls set entirely within a lower outer ring of twelve turrets, the whole encircled by a water-filled moat with a tidal dock that let ships resupply it under siege. Some three hundred firing positions could be trained on an attacker at once.

It was also never finished: the money ran out around 1330 and the walls never reached their planned height, the flawless design left forever on paper. Even so it was captured by Owain Glyndŵr's rebels in 1403 and held for two years before the English retook it, and it changed hands again in the Civil War, proof that the most elegant fortress on earth is only as strong as the garrison and the treasury behind it.

Charles IV built Karlštejn from 1348 to guard the crown jewels of the Holy Roman Empire, and its defences rise in tiers up a wooded hill, the palace lowest, then the Marian tower, then the Great Tower at the summit with walls up to seven and a half metres thick. Each stage stands higher and stronger than the last, so the treasure sat behind rings of ascending defence.

Its great trial came in 1422, when Hussite armies besieged it for some seven months and hurled dung and corpses over the walls to breed disease among the defenders, and still could not get in. The fortress held, though the jewels had already been carried to safety the year before. Karlštejn was taken only much later, by the Swedes in 1648, in the closing throes of the Thirty Years' War.

Bohus Fortress stands on a rock cliff some forty metres high where the Göta River splits to wrap it in a natural moat, its curtain walls three metres thick at the base. Small enough to be held by a modest garrison and impossible to approach unseen, it guarded the old frontier between Norway and Sweden for centuries.

It was attacked or besieged fourteen times and never once captured. In 1566 its defenders blew up a tower full of storming troops rather than yield it; in 1678 a Norwegian-Danish army of some sixteen thousand pounded fewer than a thousand defenders with over two thousand bombs for six weeks, until a Swedish relief force arrived to find the fortress wrecked but unbeaten. No enemy ever entered it as its master.

Loarre is one of the oldest and best-preserved Romanesque fortresses in Europe, an eleventh-century stronghold grafted straight onto a rocky spur of the Aragonese sierra so that its walls seem to grow from the stone, which is exactly what made it impossible to undermine. An outer ring of eight towers and a tall keep guarded the frontier against Muslim al-Andalus.

Curiously, its fearsome reputation rests on its design rather than any great battle. Built as a forward base for the reconquest of Huesca, it was barely finished before the Christian frontier swept south past it, and no serious siege is recorded. The castle was so plainly unassailable, and so quickly left behind the front line, that no army seems to have thought it worth the attempt.

Chillon rises straight from a rock island at the eastern end of Lake Geneva, deep water on one side and the mountain road on the other, so that it both guarded and taxed the vital passage between the Alps and the north. The House of Savoy turned an eleventh-century tower into a ring of curtain walls and courtyards reached only across a narrow bridge.

Its position kept it secure for centuries until 1536, when a Bernese army marching on Savoy took the castle and threw open its lakeside dungeon, freeing François de Bonivard, chained there for six years, whose captivity Byron would later immortalise in 'The Prisoner of Chillon.' Today it is the most visited historic building in Switzerland.

Trim is the largest Anglo-Norman castle in Ireland, three hectares behind a curtain wall studded with towers and entered through the first barbican gate ever built on the island. At its heart stands an unusual twenty-sided cruciform keep, raised by the de Lacy lords to hold the frontier of the English Pale.

Its story is one of repeated capture. The first timber fortress here was stormed and burned in 1173 by the High King Rory O'Connor; the stone castle that replaced it fell after several weeks' siege to William Marshal in 1224, breaking a baronial revolt; and in 1649 its garrison simply fled at Cromwell's approach, leaving it to be occupied without a blow struck.

Hochosterwitz is the storybook fortress made real, a castle on a lone dolomite crag rising 172 metres from the Carinthian plain, reached by a single path that spirals up through fourteen fortified gates, each a fresh obstacle for any attacker. Built in this form in the 1570s and 80s against the Turkish raids, its gate system is considered unique in the history of fortification.

Legend holds that no enemy ever got past the fourth gate, and the castle is remembered as one that was never conquered, though the famous gates were raised after the worst of the Ottoman raids had passed, and were never truly tested by a great assault. It is the setting, too, of the old tale of the starving garrison that threw its last ox over the wall to fake plenty, and so tricked the besiegers into giving up.

Carrickfergus juts into Belfast Lough on a rock once almost surrounded by the sea, its towering Norman keep begun by John de Courcy in 1177 and its high curtain wall later pierced with gunports for cannon, the best-preserved Norman castle in Ireland, and a garrison post for more than seven centuries.

Few castles were fought over so often. King John took it in 1210; Edward Bruce starved it into surrender after a year-long siege in 1315–16, remembered for the defenders eating their hostages; Williamite forces stormed it in 1689, and the next year King William landed beneath its walls. As late as 1760 a French raiding force captured it outright before slipping away. Strong as it was, Carrickfergus fell again and again.

Bonaguil is the last great medieval fortress of France, rebuilt around 1500 by Bérenger de Roquefeuil not against knights but against cannon: a long outer wall with over a hundred embrasures for guns, a ship's-prow keep, a rock-cut ditch crossed by two drawbridges, and casemates for flanking fire. It anticipated the artillery forts of the century to come.

And yet it never fired a shot in anger. So perfect, and so expensive, was its design that it was already obsolete by the time it was finished, and no enemy ever came to test it. Its walls were never breached; the fortress passed the centuries untouched by siege, dismantled in part only during the French Revolution, and stands as the great might-have-been of French castle-building.

Peyrepertuse is the largest of the Cathar 'citadels of the sky,' as vast as Carcassonne itself, stretched along a knife-edge limestone ridge some 800 metres up with cliffs falling sheer on either side. Its lower castle, middle enclosure and topmost keep run the whole length of the crest, guarding the old border with Aragon from a height that made a direct assault all but unthinkable.

It was never stormed. During the crusade against the Cathars its position did the fighting for it: the lord of Peyrepertuse submitted rather than face a siege, and the castle passed to the French crown in 1240 without a real fight, after which Louis IX added the upper keep and turned it into a royal frontier fortress. Impregnability, here, meant a stronghold so daunting that no one chose to attack it.