Bourtange fortification, restored to its 1750 condition, Groningen, Netherlands.
17th century map of the city of Palmanova, Italy, an excellent example of a Venetian star fort.
Historian John Lynn’s excellent term for fortifications that employed “trace italienne” bastions and other new features that eliminated “dead zones” in crossing fields of fire. Lynn also referred to these fortresses as “engineered battlefields.” They evolved in stages in reaction to improvements in 16th century siege artillery. The final form is generally conceded to have been perfected by Vauban from 1687. The evolution began with simple addition of cutaway ports and guns to existing, late medieval stone fortifications. This permitted counter-battery fire against siege engines and cannon. Next came a series of adjustments that both lowered the walls (“countersinking”) and reinforced them with earthen banks, ditches, and dry (or more rarely, wet) moats. That gave the whole fortress a crenellated appearance of alternating low walls and hard salients that were difficult to knock down with cannon and took longer still to approach with labor-intensive siege works. The new structures also allowed defensive cannon to be mounted on strong walls or inside squat towers and roundels. In addition, infantry defenders commanded fields of enfilading musket fire that daunted any brash assault by attackers. Finally, geometric bastions were built into the curtain, with more added later beyond the curtain as separate outworks. Bastions were the key innovation, maximizing the effect of sweeping fields of cross fire while defending against enfilade. These principles and design innovations led to grand efforts at complete fortification by a number of Italian towns during the late Italian Renaissance, but the expense proved so vast few were completed. The style spread outside Italy, once nearby locales such as Monferrat and Geneva built single, impressive, massive works. Other fortresses were soon built in Hungary and Dalmatia, though not as densely or as well, as the artillery threat in those theaters was not as great. The real breakthrough came along the southern border of the United Provinces, where dozens of smaller artillery fortresses were erected to provide a layered defense-in-depth that proved unbeatable by the Spanish, or later by the French. France took the lead in fortress design and construction in the late 17th century, establishing a new French school that was dominant internationally for over a century or more thereafter. Most fortresses built in northwest Europe from this time were five- or six-bastioned works mounting up to sixty cannon and perhaps 30 mortars and perriers.
A major debate has taken place among military historians as to whether or not the new artillery fortress constituted a “revolution in military affairs” that resulted in vast expansion of European armies as necessary to overcome the revolutionary effects of the new fortifications. In the 16th century the new bastions certainly restored a balance between offense and defense that had been broken by siege cannon in the 15th century. This restored balance lasted into the late 18th century. Yet, even a long-term shift in favor of defense should not be exaggerated: the Ottomans were able to overwhelm “alla moderna” (as the “trace italienne” style was known in Italy) fortresses on several occasions, using new types of cannon along with old techniques of mining and starvation. In addition the new bastions were hugely expensive: more than one petty ruler went bankrupt and lost his small state out of an effort to defend it too well. It is important to note that fortresses served an offensive as well as defensive function: they provided a base for forward operations by advancing armies. Thus, the French advanced into the Netherlands and Rhineland in the 1670s-1680s, building or securing fortresses as they moved. Similarly, the Prussians marched south into Silesia and against Austria in the 1740s, utilizing fortress bases along the way.
Trace italienne-style fortresses traveled overseas along with European trade expansion and colonial conquest. New model forts were built by the Spanish in the Caribbean, the Portuguese in Africa and India, and the Dutch, French, and English in Southeast Asia. Yet these were limited applications. In most colonies and other scattered enclaves where Europeans built artillery fortresses overseas, they did so mainly to ward off other Europeans who had modern artillery. Otherwise, old styles of fortification without full bastions usually sufficed against extant native firepower and tactics. Outside the Ottoman Empire, non- European armies during this period almost never possessed the heavy artillery needed for successful siege warfare against even older, more primitive European military architecture.
Scaling the walls of a fortification on ladders. This was a highly risky, and therefore nearly always wounding or deadly, form of assault. To counter the escalade, the revetment was often made 30 feet or more high, forcing assault ladders to become longer and hence too heavy to be raised, and the climb too long and slow for attackers to survive strong defensive fire. The practice survived invention and early diffusion of designs for the artillery fortress, but petered out over the second half of the 17th century in the face of repeated carnage inflicted on attackers by enfilade fire from bastions. In the 18th century, a few attempts at escalade were made in stealth at night, as a form of insult. One was successfully carried off by the maréchal de Saxe at Prague in 1741.
Stand-alone forts served as military garrisons and as a means of enforcing contributions in occupied territory. They provided bridgeheads across riverine frontiers or kept open traditional invasion routes, as a threat or in fact. They were positioned at the entrances to valleys, along land and river trade routes, blocking mountain passes, and across border rivers and canals. French armies simplified logistics by permitting the pre-positioning of rudimentary magazines along the line of advance or near the frontier, at jump-off points for invasions of Germany or Flanders. Under Louis XIV, the French constructed several fortified lines, including the lines of Brabant and the Ne Plus Ultra lines. Cities and major towns were also fortified, often walled or at least hosting a citadel, some from medieval times. These artillery fortresses doubled as defenses and police garrisons holding down rebellious populations. Fortresses and lines also denied or enabled collection of contributions.
Smaller European fortresses did not always follow the elaborate style of 18th-century works. And even large fortifications outside Europe might not deploy the new bastions and other artillery-fortress techniques, as they did not generally face heavy cannon other than from European (or Ottoman) attackers. During the 17th century, the Militargrenze frontier between Austria and the Ottoman Empire was spotted with 90 fortresses, but most were of a rudimentary form of bastion additions to preexisting stone, or even wooden forts. As late as the 1670s, Ottoman armies fighting in Ukraine easily overcame primitive forts made of wood-framed earthen walls. By the mid-18th century, however, all advanced militaries were heavily and lastingly influenced by the elaborate innovations introduced in the late 17th century by the brilliant Vauban, as well as his near-peers Coehoorn and Dahlberg. This presented a stepped profile, so that detached works such as ravelins could be fired over by defenders manning the rear ramparts and bastions. There was a different attitude to fortification in the east, where the Polish Army, but especially the Russian Army and Swedish Army, emphasized mobility over fixed defenses. Karl XII and Peter I went so far as to tear down existing fortifications and remove garrisons, in favor of concentrating forces in larger field armies.
Attacking a fortress or town or other military position without warning or overt preparation, usually by ruse or sudden assault. A common ploy was for disguised soldiers to jam a heavy cart inside the gate of a town or fortress so that the portcullis would not close. This seldom worked. Concealing one’s real uniform was sometimes tried on a mass scale, as when 4,000 Austrians tried to walk into Breisach disguised as French troops in 1702 (their ruse was uncovered by an alert officer). Two years earlier an Austrian force successfully made its way through an unguarded aqueduct to spring full-grown into the center of Cremona. In the mid-18th century, “insult” was achieved several times via surprise escalade, a tactic which otherwise had long since gone out of fashion. The best countermeasures against ruses and insult were alert sentries and cavalry scouting, storm bells, and maintaining a clear zone of servitude around a fortress.
The term meant “dueling field,” but became famous in reference to the open space formed between a double line of regular fortifications, part of an elaborate defense system that Vauban developed along the northern frontier of France after he broached the idea in a 1673 letter to Louis XIV. It imitated the two lines formed by infantry in battle. The pré carré on the frontier with the Spanish Netherlands linked artillery fortresses from Dunkirk through Ypres, Lille, Tournai, Valenciennes, Maubeuge, and Dinant. Among the main fortresses of the second, interior line were Gravelines, St. Omer, Aire, Arras, Douai, Cambrai, Landrecies, Rocroi, and Carleville. Its establishment involved Louis in a long-term strategy that aimed at rationalizing and straightening France’s frontiers, whether by diplomacy or, as Vauban put it, by “a good war.” The outer line was breached by the successful Allied siege of Lille (August 14-December 10, 1708). Taking the inner line was the main aim of Marlborough’s campaign of 1710. After signing the London Preliminaries, the French began work on a new set of lines, the Ne Plus Ultra. In the last campaign of the War of the Spanish Succession (1701-1714), Villars retook the lines of the pré carré, thus helping to ensure the general peace later agreed at Utrecht.
According to Geoffrey Parker in his article “The military revolution 1560–1660: a myth?”, the appearance of the trace italienne in early modern Europe, and the difficulty of taking such fortifications, resulted in a profound change in military strategy, most importantly, Parker argued, an increase in army sizes necessary to invest these forts. “Wars became a series of protracted sieges,” Parker suggests, and open-pitch battles became “irrelevant” in regions where the trace italienne existed. Ultimately, Parker argues, “military geography”, in other words, the existence or absence of the trace italienne in a given area, shaped military strategy in the early modern period. This is a profound alteration of the Military Revolution thesis originally proposed by Michael Roberts in 1955.
Parker’s emphasis on the fortification as the key element has attracted substantial criticism from some academics, such as John A. Lynn and M. S. Kingra, particularly with respect to the claimed causal link between the new fortress design and increases in army sizes during this period.
Duffy, C. (1975) Fire & Stone, The Science of Fortress Warfare 1660-1860, ISBN 978-0-7858-2109-0