The 8 strongest castles in Sweden

Bohus stands on a forty-metre rock at the fork of the Göta River, which splits to wrap the fortress in a natural moat; its curtain walls run up to three metres thick, and successive kings layered bastions and outworks onto the medieval core. Built by Norway and long held by Denmark-Norway, it commanded the contested corner where three kingdoms met.

It was besieged or attacked fourteen times and never once taken. The hardest test came in 1678, during the Scanian War, when a Dano-Norwegian army of some fifteen thousand under Gyldenløve battered fewer than a thousand defenders for weeks; a mine brought down a bastion and the walls were left in ruins, but a Swedish relief force arrived to find the garrison wrecked yet unbeaten. No enemy ever held Bohus.

Kalmar guarded Sweden's southern frontier with Denmark, and the Vasa kings rebuilt the medieval castle into one of Scandinavia's most advanced Renaissance fortresses. The Pahr brothers girdled it with angled artillery bastions and round gun towers set to sweep the walls and the sound; a broad moat ringed the island, and by the early 1600s the works mounted close to three hundred cannon.

It was besieged again and again across the border wars. In the Kalmar War the Danish king Christian IV brought six thousand men to the walls in May 1611, and the commandant surrendered the castle that August; Sweden recovered it at the 1613 peace. Fought over more than almost any Swedish stronghold, it took and returned artillery fire for two centuries.

Malmöhus sits on its own island, Slottsholmen, the oldest surviving Renaissance castle in Scandinavia, raised for the Danish crown from 1537 to control the Öresund and its tolls. Two heavy round gun towers anchor the wings, and after Sweden took Scania in 1658 the fortress was modernised on the Dutch bastion system into a front-line national stronghold facing Denmark.

That work was tested in the Scanian War. Between 11 June and 5 July 1677 Christian V of Denmark bombarded town and castle with dozens of siege guns and mortars and stormed the walls; the garrison threw the assault back and the Danes withdrew beaten. Malmö was the one Swedish stronghold in Scania the Danes never managed to take.

Begun around 1411 by Erik of Pomerania, king of the Kalmar Union, Visborg grew into one of the largest and strongest fortresses in the Baltic, thick walls, multiple towers and deep outworks guarding the harbour and dominating the merchant town of Visby. Deposed as king, Erik held out here and turned to piracy in the Baltic before ceding the castle to Denmark in 1449, and it stayed a Danish stronghold on Gotland for two centuries. Its end was demolition, not defeat: when Danish troops withdrew after the 1679 Treaty of Lund they deliberately blew the fortress up so Sweden could never use it, leaving only the wall fragments that overlook the port today.

Borgholm commands a limestone ridge on the west coast of Öland, looking out over the Kalmar Sound, a strong medieval stronghold that the Vasa dynasty rebuilt and that Charles X Gustav recast in the 17th century as a vast Baroque fortress-palace with round corner towers, its scale still overwhelming in ruin. The military record is harder to flatter: the castle changed hands repeatedly in the Danish wars, falling to Denmark in 1510 and 1520 before Gustav Vasa recovered it in 1523, and in the Kalmar War it surrendered to the Danes in 1611 and again in 1612 after a two-week siege. Fire gutted it in 1806. Impressive in scale and position, but a place more often taken than held.

Örebro Castle sits on a small island in the Svartån, the river forming a natural moat around four thirty-metre round towers and a thick ring wall that guarded the crossing on the road north. From a medieval keep it grew into a full fortress and then a Renaissance stronghold under the Vasa kings. It was besieged at least nine times and fell twice: Christian II of Denmark seized it in 1520, and Gustav Vasa retook it after a long blockade in 1522. A genuine moated island fortress with a real war record, if lighter in its engineering than the great bastioned border strongholds.

Vadstena was purpose-built as a modern artillery fortress: Gustav Vasa began it in 1545 to shield the Swedish heartland from Denmark and the unrest of Småland, ringing it with three wide wet moats, around thirty metres across, a curtain wall, a gatehouse and four circular cannon towers on the shore of Lake Vättern. On paper it is among the most complete Renaissance gun-fortresses in Sweden. In practice it was never seriously tested: no enemy army ever laid siege to it, and by the 1600s it was sliding from stronghold to royal palace and later a grain store. Strong by design, but unproven in war and weak in its flat lakeside position.

Nyköpingshus began as a 12th-century royal castle at the river mouth, was enlarged by Birger Jarl, and was turned by Duke Charles from a stern medieval stronghold into a Renaissance palace. Its fame is political rather than military: at the 'Nyköping Banquet' of 11 December 1317 King Birger seized his brothers, dukes Eric and Valdemar, and left them to starve in the dungeon, a coup that triggered a revolt in which the castle was stormed and largely wrecked in 1318. A great fire gutted it in 1665 and it never recovered as a fortress. A powerful royal seat in its day, but a ruin remembered for a murder, not a siege.