The 8 strongest castles in Switzerland

Aarburg is the heaviest piece of military engineering on this list, a limestone keep with walls 3 to 3.5 metres thick, its lowest floor cut straight from the bedrock, set on a steep rocky spur above a narrow pinch of the Aare. Bern rebuilt the medieval castle into a full artillery fortress across the 16th and 17th centuries, the baroque works of 1659–1673 wrapping the crag in heavily fortified ranges to guard the road between Protestant Bern and Zurich.

For all that bulk its strength was rarely tested and never proven. The medieval castle fell to Bern after only a brief siege on 20 April 1415, and when the French army arrived on 10 March 1798 the great fortress surrendered without a fight. Its rank rests on the scale of its defences and its commanding position rather than on any siege it actually withstood.

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 it both guarded and taxed the passage between the Alps and the north. The island leaves no ground for siege engines or mining; an attacker had only a narrow causeway to reach a ring of curtain walls, towers, machicolations and arrow slits, later fitted with gunports for cannon.

The position held the castle for the Savoyards for centuries, until a Bernese army marching on Savoy took it after a short siege on 29 March 1536 and threw open its lakeside dungeon. It has stayed in Swiss hands ever since. Few positions here are as naturally defensible, but as a compact medieval water castle it is a lighter fortress than Aarburg's artillery citadel.

Tourbillon was the bishops' war-castle, raised from about 1294 on a steep rock 182 metres above Sion and reachable only from east or west, its crest ringed by crenellated walls, watchtowers and gated approaches. This was no ornament: the garrison kept more than 5,000 crossbow bolts and several thousand trebuchet stones ready behind the walls.

It was fought over in earnest. During the Raron affair of 1417 the townspeople stormed and burned it, cracking the walls and gutting the interior, after which it was rebuilt around 1440–1450. What finally ended it was not a siege but the accidental town fire of 24 May 1788, which took the roofs and floors and left the shell that stands today.

Tarasp commands the Lower Engadine from a rocky hill roughly 100 metres above the Inn, a strong natural position its owners reinforced with a ring wall, a zwinger and half-towers. Held for Austria on the far side of the valley from its Protestant neighbours, it was genuinely fought over: local Reformed forces attacked it in 1548 and again in 1578 without success, and it stayed in Austrian hands until 1803.

Its defences were beaten only once, when Engadine Protestants stormed and burned the castle in 1612. Much of what stands now is a thorough restoration of 1906–1916, but the crag and the record of sieges resisted are real, and they place it above the quieter castles below.

Thun's strength is one great object: the huge rectangular keep raised by Berthold V of Zähringen around 1180–1190, a hall-block with a tower at each of its four corners, dominating the town and the river narrows below. As a donjon it is formidable, but it was built to overawe a region rather than to survive repeated assault, and its military story is correspondingly quiet, it passed to Bern in 1384 by cession after the Kyburgs lost the Burgdorf war, not by storm. A commanding seat of power, but with little true siege record to its name.

Laufen sits dramatically on the cliff directly above the Rhine Falls, a site first fortified more than a thousand years ago to watch the river and its crossing. The waterfall and gorge give it a striking natural edge, but the castle itself is a modest stronghold rather than a great fortress, and its walls did not always hold: in 1449 Zurich besieged and took it, the defenders escaping by rope down the cliff into the Rhine and swimming to the far bank. It owes its fame far more to its position over the falls than to any weight of defences.

Valère is really a fortified church rather than a fortress. The Romanesque basilica of Notre-Dame crowns the hill facing Tourbillon across Sion, and the chapter that lived there did wall the summit, outer ramparts, corner towers and inner gates, and kept a cistern and grain mill so the community could hold out through a siege or an epidemic. But those defences were built to shelter clergy, not to command a battlefield, and the site has essentially no record of being besieged or stormed. Its place here rests on passive strength and position, not on any fighting past.

Habsburg is famous for its dynasty, not its defences. Count Radbot's tower on a low rise above the Aare, built around 1020–1030, gave the family its name, but it was always a small ancestral seat, and by about 1220–1230 the Habsburgs had already outgrown it and moved down to Brugg. It was never a major stronghold and saw no significant siege; the feuds of the age rarely involved storming a rival's castle, and this one had little to storm. It ranks last as a fortress precisely because it was built as a modest lordly residence, and the family that made it legendary left it behind.