The 10 strongest castles in Italy

The Sforza Castle grew into one of the largest citadels in Europe. Its Visconti core was a 200-metre square with four corner towers and walls up to seven metres thick; Francesco Sforza added the ghirlanda, an outer wall behind a water ditch, and under Spanish rule the whole was wrapped in a twelve-bastion star fort whose outworks ran some three kilometres and covered 26 hectares. Its one weakness was the ground: flat Lombard plain, no natural strength at all.

For all that mass, Milan's fortress was fought over and fell again and again through the Italian Wars. The French took it from Ludovico il Moro in 1499; in 1515, after Marignano, Francis I set sappers to mine the foundations and the garrison capitulated; it changed hands once more in the imperial campaigns of 1521-22, the year the Torre del Filarete, then a powder magazine, simply blew up. Vast and sophisticated, but never a fortress that held.

Fort Bard plugs a narrow gorge of the Aosta Valley, its batteries stacked in tiers on a rock above the Dora Baltea, commanding the only road between France and the Po plain. In May 1800 the old fort earned its fame: barely 400 Austro-Piedmontese under Captain Bernkopf held Napoleon's 40,000-strong Army of the Reserve for close to two weeks. The French had to manhandle their guns past it along a mule track by night; the fort fell only on 1 June, after a heavy cannon breached the walls, and the garrison marched out with the honours of war.

The fort standing today, though, is not the one that stopped Napoleon: he had that razed as a 'vilain castel'. What replaced it, a vast three-block fortress of 283 rooms and fifty casemated gun-ports, rebuilt by Charles Albert of Savoy between 1830 and 1838 against a French return that never came, has never once been attacked.

Charles I of Anjou raised the Castel Nuovo over the Naples waterfront in 1279-82, and the Aragonese turned it into a serious fortress: five colossal cylindrical towers faced in piperno stone, curtain walls thickened inside and out, anchoring the city's defensive line beside Castel dell'Ovo and Castel Capuano.

Grand as it was, it stood on open ground by the harbour and was taken more than once. Louis I of Hungary sacked it in 1347, and it was besieged and captured again in 1348. In 1442 Alfonso V of Aragon seized Naples after his men crept in through an old aqueduct, and the cannon-scars of these fights are still legible on the marble gate. A royal stronghold, but not an unbreakable one.

San Leo sits on an isolated block of rock 600 metres up, ringed by vertical cliffs on every side, and for centuries it looked impregnable. Otto I of Germany had to besiege it for three years, 961-963, while it served as the last capital of Berengar's Italy. Later Federico da Montefeltro brought in Francesco di Giorgio Martini to recut it for gunpowder, with sloped bastions and batteries able to answer fire in several directions.

The impregnable reputation is largely legend. The Malatesta seized it in the 14th century; in 1441 the young Montefeltro took it back by sending men to scale the sheer cliff at night; and in 1502 Cesare Borgia had it too, holding it until Pope Alexander VI's death in 1503 returned it to the Montefeltro. A magnificent natural stronghold, repeatedly proven takeable.

Castel dell'Ovo is the oldest castle in Naples, planted on the islet of Megaride with the sea on every side, the best natural position of the city's three fortresses. The Aragonese lowered its towers and turned its guns to face the land as artillery changed the rules. That prudence was tested in 1503, when Gonzalo Fernandez de Cordoba's Spanish siege drove out the French; the bombardment shattered what remained of the towers, and the castle was afterwards rebuilt with thick walls and octagonal bastions. Strong by nature, but not proof against cannon.

Gradara was the Malatesta stronghold, its keep wrapped in a double ring of walls running some 800 metres, the outer line meant to break an assault before it reached the inner. Its finest hour came in 1446, when Sigismondo Pandolfo Malatesta held it against Francesco Sforza: the besiegers sat before the walls for forty days and withdrew without taking it. The defences were real but not invincible, for in 1463 Federico da Montefeltro, leading papal troops, captured the rocca and handed it to the Sforza of Pesaro. A hilltop double-walled fortress with one siege withstood and one lost.

The Castello Estense is a moated quadrilateral dropped into the middle of Ferrara, four heavy corner towers behind a wide water-filled moat crossed only by drawbridges and covered by ravelins. Bartolino da Novara began it in 1385, and its purpose is telling: it went up after a mob had lynched a ducal tax official that May, so the Este could hold their own city as much as repel an outside army. No great siege ever tested it; its strength was the moat, the towers and the message they sent, and it stayed the seat of Este power rather than a battlefield.

Castelvecchio was raised by Cangrande II della Scala from 1354, two walled wards on the Adige joined to a fortified bridge whose 48-metre central arch was the widest brick span of its day. Tellingly, that bridge was an escape route, letting the lord flee north toward Tyrol if his own Veronese turned on him, so the castle guarded as much against the city as against invaders. It never made its name withstanding a siege. French troops sacked it in reprisal after the anti-French rising of 1797, and the retreating German army blew the bridge in 1945, rebuilt in 1949. Solid, but a residence-fortress more than a tested stronghold.

The Scaligero Castle guards the neck of the Sirmione peninsula on Lake Garda, water on almost every side, with a rare walled harbour, the darsena, that sheltered Scaliger and later Venetian galleys and ranks among the oldest surviving fortified ports in Italy. Built by the della Scala after the mid-14th century, it was a lake toll-post and naval base more than a heavy siege fortress: three towers, a tall keep and a swallowtail-battlemented curtain, but no real record of standing off an army. Its defence was the water and the harbour it controlled, not walls built to soak up bombardment.

The Rocca Borromeo stands on a rocky spur above Angera, its turreted wall running out to the cliff edge over Lake Maggiore, a commanding seat if a modest fortress. It changed hands by politics and purchase, never by storm: the Della Torre lost it to the Visconti after the Battle of Desio in 1277, and in 1449 the Borromeo simply bought jurisdiction over Angera for 12,800 lire. There is no famous siege in its record. Part stronghold, part frescoed noble residence, the Visconti even had their victory over the Torriani painted on its walls. It is the lordly seat on this list, not the hardest fortress.