The 7 strongest castles in Czechia

Charles IV raised Karlštejn to guard the imperial crown jewels, and its defences climb a wooded hillside in stepped terraces, the imperial palace low down, the Marian tower above it, and the Great Tower crowning the summit with walls up to seven and a half metres thick. Each level had to be carried before the next, forcing any attacker uphill under fire.

Its great trial came in 1422, when Hussite forces under Sigismund Korybut besieged it for roughly seven months, hurling dung and some 2,000 cartloads of corpses and filth over the walls to breed disease, and still could not break in. No medieval army forced it; its defensive life ended only with the Swedes late in the Thirty Years' War, around 1648.

Špilberk commands the hill above Brno, and after the town bought it in 1560 it was wrapped in bastioned artillery fortifications that turned a medieval castle into a full baroque citadel, the strongest position in Moravia and, later, one of the Habsburgs' most feared state prisons.

Its defining hour came in 1645, when Torstenson's Swedish army, perhaps eighteen times the defenders' number, besieged Brno and Špilberk from May to August. Raduit de Souches held with barely 1,500 men, only a few hundred of them trained soldiers, and after a failed general assault on 15 August the Swedes broke off and withdrew on the 23rd. The citadel was never stormed.

Known as 'the king of Czech castles,' Zvíkov sits on a steep, hard-to-reach promontory above the meeting of the Vltava and Otava, with water and rock guarding it on most sides. Its 32-metre bergfrit, the Hláska, anchors walls that were later thickened to carry heavy artillery.

Twice it proved the position. A four-month Hussite siege in 1429 failed outright, and in 1618 a garrison of about 140 men held off some 4,000 Habsburg troops. It was never taken by storm, the defenders only gave it up on terms in October 1622, after which it was plundered.

Loket coils inside a tight bend of the Ohře, the river wrapping it on three sides below thick stone walls, the position that earned it the names 'Key to the Kingdom of Bohemia' and 'the impregnable castle.' The Hussites tested it twice, under Krušina of Švamberk and then Jakoubek of Vřesovice, and were beaten off both times. The 'impregnable' label is partly tradition, though: during the Thirty Years' War the town and castle were repeatedly besieged and finally taken by the imperial army, and later menaced by the Swedes.

Křivoklát was a royal stronghold deep in the hunting forests west of Prague, built around a monumental great tower and heavy Gothic walls, and trusted for a time to hold the crown jewels. But its war record is more mixed than its bulk suggests: during the Hussite Wars it changed hands, taken by both Hussites and Catholics rather than standing off a great siege, and in later centuries it declined into a harsh prison and burned more than once. A powerful keep, but never a proven siege-breaker.

Kost hides not on a hill but on a spur between converging sandstone gorges, so attackers often saw it only at the last moment, simply reaching it was the hard part. Its Gothic donjon, the White Tower, is set on a trapezoidal plan with the corners turned toward the likeliest line of catapult fire to deflect the stones, all behind a double ring of walls. It is remembered as never conquered, but that reputation rests as much on its concealed siting and legend, the tale of Žižka calling it 'hard as a bone', as on any well-documented siege, and the Hussite assault of that story is not firmly attested.

Bouzov has genuine medieval roots, first recorded in 1317, and the birthplace of the future king George of Poděbrady in 1420, but the castle standing today is largely a romantic recreation. Between 1895 and 1910 the Teutonic Order rebuilt it wholesale in neo-Gothic style, complete with running water and central heating, leaving little original fabric behind. It never withstood a famous siege, and on fortress merit it ranks last here, judged on its real defences rather than its picture-book silhouette.