Depiction of artillery in an illustration of the Siege of Orleans of 1429 ( Martial d’Auvergne, 1493)

The rounded walls of the 14th century Sarzana Castle showed adaption to gunpowder.

At the end of the Middle Ages, castles began to lose their military function, but not their psychological impact as a symbol of authority. Gunpowder and cannons supported armies of mercenary troops, and the garrison forts built to house them adopted the crenellated walls of private aristocratic castles. By the sixteenth century, professional soldiers lived in barracks, a few officers and the governor had finer quarters, and kings and nobles merely directed the operations from distant palaces where battlements had become purely symbolic decoration. The Battle of Crecy between France and England in 1346 is traditionally considered to be the first use of cannons on the battlefield. At first the noise and smoke created by the explosion terrified horses and men, and wreaked more havoc than the projectiles. Early cannons could be more dangerous for the gunners than for the enemy, but military engineers rapidly developed the weapons’ power and accuracy. A castle’s high walls and towers made easy targets for gunners whose power and accuracy reduced once formidable medieval buildings to rubble. Mining became more successful because the attackers could put explosives under the walls.

Changing Castle Design

With cannons, siege warfare and castle design had to change. Stone-throwing machines were still very effective, but the prestige attached to cannons because of their novelty and their enormous expense made them the ultimate royal armament. These early cannons could be fired only ten or twenty times an hour and had to be cleaned after every shot and regularly cooled. They were effective only at about fifty yards. Cannons required massive earthworks to absorb the shock of firing.

Mons Meg, the six-ton cannon still to be seen in Edinburgh castle, was cast in 1449 in Flanders for the duke of Burgundy, who presented it to the Scottish king in 1457. Mons Meg could fire gunstones that weighed 330 pounds nearly two miles, but the cannon was so heavy it took 100 men to move it and then they could move it only at a speed of three miles a day. The Scottish kings used Mons Meg as a siege weapon for the next hundred years, as much for the impressive explosion it produced as for its actual usefulness. After about 1540 the cannon was only used to fire ceremonial salutes from Edinburgh castle walls. In 1681 the barrel burst and could not be repaired.

To counter the new offensive weapons, architects created a new system of defense in depth by using low, broad ramparts that were wide enough to endure firing from the enemy and at the same time support their own cannons and teams of gunners. Extremely thick masonry walls were expensive and slow to build, so wide and low earthen ramparts faced with stone became common. Since guns shoot horizontally, the land around the castle walls was cleared to form a space called the glacis. As we have seen at the castle of Angers, existing towers were cut down to the same height as the walls and turned into firing platforms. This redesign of the towers did not “slight” the castle, but rather made it more effective in the new age of artillery warfare.

Batteries and Bastions

Between 1450 and 1530 Italian military engineers, architects, and theoreticians rethought castle design. To be most effective, guns were placed in batteries so that several cannons fired together at the same spot. Low, solid, D-shaped towers together with masses of masonry angled out from the walls served as supports for artillery and as observation platforms. This new form of military architecture was called the bastion system. At first the bastions had a pentagonal plan: two sides form a point facing toward the enemy, two sides slope back toward the wall, and the fifth side adjoins the wall. Protective ears protruded at the angles. A curtain wall joined two bastions so an enemy approaching the curtain wall came under fire from the flanking bastions, and each bastion protected its neighbor as well as the wall. The units could be repeated around a castle or city. The developed gun platforms were called a bolwerk in Dutch, and a boulevard in France. They were built as ramparts all around the castle or town often as a second line beyond the old walls. In the nineteenth century, when city walls and ramparts were removed and the space was turned into tree-lined avenues, the avenues continued to be called boulevards. Today one can trace the line of these defenses on a city map by following modern boulevards.

The Emerging Fortress

Based on geometry as much as local conditions, the design of bastioned fortresses became the province of specialists whose plans might be based on theory rather than topography. Italians devised wholly “rational” plans for fortresses and cities in which geometric figures, especially stars formed by lines of fire, determined the plan of glacis, wide moat, and ramparts. But the development of printing in Germany and soon throughout Europe meant that Italian theories and designs spread rapidly and relatively cheaply. The plans, beautiful as designs and drawings in themselves, were often too fanciful or expensive to be built.

The sixteenth century was an age of wide-ranging and talented theorists. Men we usually think of as painters and sculptors also designed fortifications. Leonardo da Vinci (1452-1519) worked in Milan from 1482 to 1498 for the ruling Sforza family on military and engineering projects. Leonardo also designed guns, crossbows, armored vehicles, submarines, a parachute, and a flying machine and made plans for fortresses. From 1502 to 1504 Leonardo worked in Florence as a military adviser, then returned to Milan to advise on castles from 1508 to 1513. From 1517 until his death in 1519 he lived in France in the service of Francois I. Another Italian, Francesco de Giorgio (1439-1502) wrote a treatise on military engineering with improved fortress designs, published in 1480. From 1480 to 1486 he served the Duke of Urbino, designing the fortifications of Urbino. By 1494 de Giorgio was working for the king of Naples and Sicily designing the fortifications in Naples. Even Michelangelo (1475-1564) was the military adviser to the city of Florence in 1529, and in 1547 he designed the Vatican defenses.

The leading architectural writers and theoreticians, like Leon Battista Alberti (1404-72), devised an ideal symmetrical plan for forts and cities. The Italians eventually settled on the five-point star as the ideal shape. The streets radiated out from a central command post or headquarters (or city center with market hall and church) with streets leading to gates or the bastions. Streets in concentric circles completed the internal division. The ideal plan did not allow for individual variations; consequently, it never developed successful cities, but it could be found in army installations. In the sixteenth and seventeenth centuries the Italian designs spread through Europe and the European colonies.

The French architect and military engineer Sebastien Le Prestre de Vauban, who built major fortresses on the French borders for Louis XIV, became the most skillful designer of fortresses using the bastion system. The first forts in the Americas-Louisburg in Nova Scotia, Canada, or Fort Augustine in Florida-are simple “provincial” examples of the Vauban fort. Fort McHenry in Baltimore, where The Star Spangled Banner was written, is a characteristic example of the bastion scheme with its central plan, wide earthen ramparts, bastions, and casemates. The Pentagon repeats the Renaissance five-sided, pentagonal plan with a central court, radiating street-like halls and concentric corridors. The castle design recommended by Leonardo da Vinci and Alberti has become the American headquarters and symbol of military power.