Although the Napoleonic wars produced some of History's most dramatic pitched battles, the fortresses of Europe, both large and small, still played a significant role in almost every campaign that was conducted during this era. Napoleon first made his mark at the siege of Toulon. The battles of Castiglione, Arcola and Rivoli were fought with the great fortress of Mantua and the sovereignty of northern Italy as the prize. Massena's famous defence of Genoa was the key to Napoleon's success at Marengo, and no story of the Peninsular War would be complete without due reference to the savage struggles for Saragossa, Badajoz, Ciudad Rodrigo and Burgos. The list of sieges and battles fought for the capture or relief of strategically important fortresses would fill many pages.

Because of their important considerable amounts of time, thought, labour and money went into the science of fortress construction. So highly regarded and so technical a subject was fortress construction that some of Europe's foremost universities boasted a Chair in Fortification. As with other sciences, the basic principles of fortification can be clearly defined.

DEVELOPMENT OF FORTIFICATION

Ever since the gradual adoption of artillery as the principal weapon of the besieger, fortress construction had under gone a series of relatively rapid evolutionary developments. The first and most obviously noticeable effect of artillery fire was its ability to smash a hole in the walls of fortification, but of almost equal importance was the use of enfilade or flanking fire. Well directed flanking fire along a straight line of ramparts could have a devastating effect upon the defenders. The result of these two methods of fire tactics - direct and enfilade - was that the complete design and profile of fortresses was re-thought.

The fundamental structural feature which distinguishes a `modern' fortress from a pre-artillery work is the bastion. These were angular projections forming part of the main defences - the enceinte - of a fortress. Because they project the ramparts of the walls from enfilade fire, but also they permit the use of enfilade fire from their battlements upon any enemy body attempting to approach the curtain. Bastions were first used in fortress construction in the early 16th century, and were small and widely placed. With improvements in the effectiveness of firearms, due to the introduction of the flintlock, bastions, by the end of the 16th century, were spaced within musket range of each other so that all the ground between the bastions could be covered by enfilade fire.

It was observed that high, open, masonry walls, no matter how thick, were easily pierced by the constant battering of heavy calibre guns. The walls, therefore, had to be protected and this was accomplished by the building of large, sloping earthen banks in front of the walls. The effect of striking the ground with a heavy iron ball was to make the earth even more compact, and this effect was heightened by the fact that the banks were sloped, causing the shot to bounce up the slope rather than bury itself into the ground.

The creation of a glacis was comparatively inexpensive, requiring no specialist labour such as masons nor the importation of costly building materials. The glacis was always stripped of cover to allow the defenders a clear field of fire. Due to the resilience and availability of earth, the main ramparts also came to be built of earth cut vertically and merely faced with stone. The earth for the ramparts was found by the digging of a ditch beneath the main walls, and the ditch, which was sometimes flooded with water, formed a further defensive barrier.

Design and Contruction of Fortresses Brief Analysis by John Grehan

Introduction and Development
Construction
Glossary