Development of Siege and Fortress Artillery

Fortifications and siege works. (American Artillerist’s Companion)

Construction of fortified bridgeheads (têtes du pont). In the centre of the second row is an excellent representation of a horn work. (American Artillerist’s Companion)


When a man has committed no faults in war, he can only have been engaged in it but a short time.

Marshal Turenne

The ring of hammers and other blunt objects, heavy digging of field fortifications, many times under fire, the building of gun platforms in almost every type of terrain, including muddy, flooded ground, marked the beginning of a siege of a fortress or a strongly fortified city or town. Engineer officers would direct the beginnings of the siege with their templates and instruments, calculating mathematically where to dig and, with their brothers of the artillery, where to emplace the siege batteries to bring the fortress under punishing fire.

Engineer troops, the sapeurs du génie and miners, would prepare their work, the miners getting ready once again to sink their shafts and begin their tunnels toward the fortress to their front and preparing the mining charges that could bring down the curtain walls confronting them. The sapeurs would don their blackened armour, cuirass and lobster helmet, that might, or might not, protect them in the besiegers’ trenches against gunfire from the defenders, and prepare to dig saps and parallels and perhaps lead the infantry assaults.

With the initial saps and approaches dug, the first batteries established with their wooden firing platforms and magazines, the great guns would be brought into position by horse- and man-power, within range of the opposing fortified positions to begin their relentless pounding of the enemy positions both day and night. Siege guns, 16- and 24-pounders, coupled with 8-inch howitzers, would blast the defenders and the great mortars, lofting their deadly bombs over the fortress walls and into the interior would search for the fortresses’ magazines for a lucky shot that might end the siege.

Last of all, but not nearly least, the infantry battalions, when not engaged in digging the siege entrenchments in support of the engineers, would wait until summoned to assault breaches made in the fortress walls if the fortress did not capitulate before that was necessary. The ‘poor bloody infantry’ would bear the burden, and pay the price in blood, for any failure of the engineers, artillerymen, and the senior officers if the siege had not been properly handled before the infantry were sent in.

With the advent of gunpowder artillery in Europe in the fourteenth century, a balance was usually attempted, and many times achieved, between firepower and mobility. Field artillery came into its own by the middle of the fourth decade of the eighteenth century, pioneered by the Prussians, with the Austrians making similar changes in the next decade. The French followed in the mid-1760s after humiliating defeats in the Seven Years War that clearly demonstrated the inferiority of the then-current Vallière System of Artillery of 1732. Just about every other nation with an interest in artillery followed suit, including the young United States upon declaring independence from Great Britain in 1776.

Heavy artillery, however, was present from the dawn of the arm, and that was a function both of technology, or lack of it, and the need to have guns strong enough to punch through or partially demolish both permanent and field fortifications. Heavy artillery is the main subject of this volume, with its strength and lack of general mobility and inability to keep up with a fast-moving field army being its main characteristics.

The main opponent of siege artillery was fortress or garrison artillery, usually composed of the same guns as siege artillery, but mounted on different gun carriages, designed to be operated inside fortifications and to defend the position where they were emplaced.

Siege and fortress artillery also included howitzers and mortars. The howitzers used in siege and fortress operations were of the same general design as those assigned to the field artillery, but were larger and heavier, with the same restrictions on movement as siege artillery guns. Mortars were stationary artillery pieces, designed for the attack and defence of fortified places, and ranged from small to large and generally speaking fired explosive shell. Howitzers were something like smaller mortars, but mounted on field carriages, and were somewhat more mobile than the mortars.

All siege artillery would be mounted in batteries supervised and constructed by the engineers and artillery officers, and great wooden platforms would be emplaced from which the artillery could fire from a stable position.

Sieges were usually carefully undertaken, meticulously planned, and were methodically carried out with the besiegers’ trenches and batteries edging ever-closer to their targets and objective. While the artillery rate of fire might be much slower than that of field artillery in battle, it was relentless and would continue day and night until a breach was made in the curtain wall or the defenders finally capitulated.

The initial siege works and artillery batteries and firing positions completed, sweating gunners manhandled their large, awkward siege pieces onto the firing platforms, managing to get the long gun tubes into the embrasures cut into the field works without damaging the entrenchments. Ammunition would be moved into the magazines constructed in the rear of each siege battery position, dug in and protected from enemy artillery fire. Artillery implements would be placed in each gun position, for the gun crews to use in pointing, loading, and cleaning each piece. The gun crews were smaller than those for field artillery, even though the heavy siege guns were both physically larger than the field pieces, and the guns themselves were of larger calibre.

Large mortars were emplaced in some of the siege battery positions. Of larger calibre than even the largest of the siege guns, mortars would lob bombs over the walls of a besieged fortress, town, or city. These were huge compared to the ammunition fired by the siege guns – some weighing in at 200 pounds. Their crews were also smaller than those in the field artillery, as the mortars were stationary weapons, the guns tubes emplaced in their ‘beds’ – heavy, awkward mounts. Whereas the siege guns were on the familiar wheeled gun carriages which could be moved as necessary, the huge-mouthed mortars would have to be moved by specially constructed vehicles from place to place, and then assembled in their prepared firing positions.

Together, the mortars and heavy siege guns, usually known as ‘battering pieces’ would concentrate their firepower against a pre-selected point of the besieged place to prepare it for an infantry assault or to batter the garrison into submission.

Fortress and Siege Fortifications and the Attack and Defence of Places

The fate of a nation may depend sometimes upon the position of a fortress.


13 October 1810, Sobral, Portugal

Chef de Bataillon Jean Jacques Pelet, first aide-de-camp to Marshal André Massena, commander of the Army of Portugal, and his companion, Capitaine Jean Richoux, made their way towards Sobral by taking a steep and narrow road up to a position from where they could observe the British fortifications that were becoming known as the Lines of Torres Vedras.

While the road had been repaired in places, it was a difficult climb that was hard on the horses, and by the time they reached their objective, only one of the dragoons remained and his mount had thrown a shoe. Pelet and Richoux dismounted and were guided to the top of a hill by some Portuguese peasants, who were, however, very closed-mouthed even as to the names of the villages in the area.

Being an engineer, Pelet closely inspected the terrain and noted that the French maps were inaccurate and needed to be updated. French troops were occupying the area, and Pelet and Richoux picked up another escort, this time of voltigeurs. These light infantrymen, often called kleine Manner (‘little men’) in contemporary comments, were efficient and excellent escorts for the type of terrain the two staff officers had to negotiate on their reconnaissance.

The defences were extensive, and were manned by both Portuguese and British troops, and they would definitely be a hard nut to crack if Massena chose to assault them. A mixture of fortifications had been constructed – redoubts, lunettes, redans and trenches criss-crossed the rough terrain, and all of them appeared to be mutually supporting.

When he had seen enough, Pelet motioned for them to go, and he and Captain Richoux with their escort of vigilant voltigeurs, made their way back down to friendly territory. Massena would not like their report, but would take it to heart and no doubt, as per his usual practice, he would make his own reconnaissance. Massena was no fool. He was a good commander who could be ruthless when need be, but he would not waste his troops in useless assaults against what appeared to be an impregnable position.

Since the dawn of warfare, man has attempted to protect himself and what is his with some type of fortification. Alexander and his near-invincible Macedonians were successful in the attack of fortified positions, be they temporary or permanent. The Romans were excellent military engineers and understood in depth the defence and attack of places. In the Middle Ages the fortified castle could sometimes withstand a siege, especially if the garrison had enough provisions and access to a potable water supply. With the introduction of gunpowder artillery in the fourteenth century, castles could now be breached more easily, and it was gunpowder artillery manned by the Ottoman Turks that finally defeated the walls of Constantinople in 1453, arguably the most sophisticated defensive system up to that time, the Eastern Romans being the capable inheritors of the Roman ability and flair for military engineering.

Recognizing that modern artillery had rendered the older systems of fortifications obsolete, such military engineers as Vauban and Coehorn developed fortification systems that were lower, harder to breach, and usually were organized and defended in depth.

There are generally speaking two types of fortifications – permanent and temporary. Permanent fortifications usually took the form of the large masonry defences of fortified cities and major fortresses. These required constant maintenance because if left alone they would fall into disrepair. Despite their imposing appearance and apparent strength and impression of solidity, masonry and brick fortifications could be quite fragile. Temporary fortifications took the form of earthworks, and these could be built for use on a battlefield and take the shape of anything from a strong redoubt, to redans, flèches, and lunettes that would be hastily constructed in a battery position by artillery gun crews. Some temporary fortifications could be used as semi-permanent structures, such as those used to fortify a bridgehead, or those made in the breach of a besieged fortress after an artillery bombardment had punched a hole in the curtain wall.

Interestingly, earthworks were also used in permanent fortifications either to enhance the masonry works or to repair them. They were also used to construct new defensive works during a siege to replace works that had been breached or destroyed.

Siege works were also semi-permanent field fortifications and were constructed of earth and wood. Siege batteries would be built of earth reinforced with gabions or wood. Embrasures for the siege guns would be earth reinforced with wood. and the gun platforms inside the works, essential for stable firing positions for siege artillery, were constructed of wood.

Fortresses filled more roles than merely defensive structures. They served as depots and magazines and would be filled with supplies during a campaign, especially along an army’s line of communication. They could be garrisoned by regular troops, but these would usually be forwarded to the field army, and their place taken either by recruits or conscripts who would then complete their training before being sent forward as replacements when needed or requested.

Fortresses were usually ‘easy’ to defend against an attacking or besieging army, and it was a long, tedious process for an army to prepare to besiege a fortress, especially a fortress city. Just to invest and surround a fortress took a large number of troops and units, and it also took time to prepare the siege works. Many times defences had to be prepared by a besieging army to protect itself from an army marching to relieve the siege. Sometimes, sieges would be lifted by the besieging force having to march against an enemy army intent on relieving the fortress, which was done during one of the British sieges of Badajoz in 1811, resulting in the bloody battle of Albuera between Marshal Soult’s French and British General Beresford’s British and Portuguese.

The Fortress

When gunpowder weapons, especially artillery, were developed in the late Middle Ages, all existing fortifications soon became obsolete. What resulted was a new range of permanent and field fortifications which, if not impervious to artillery fire, then at the very least made it more difficult for artillery to breach permanent defences. The use of earthworks became more frequent over the years, but permanent masonry fortifications were developed that would give the defender at least a chance of withstanding modern artillery fire.

Overall, one of the best concepts of defensive works was to construct them in depth which gave the attackers the problem of overcoming defences in layers and in order to accomplish that mission they might incur heavy enough casualties to cause the siege to fail.

The great objective of fortifications and the artillery that one employs as the principal agent of their defence is to make one’s troops, which are inferior in numbers, in morale, or in skill of manoeuvring, more able to resist another’s troops which are superior in one or another of these points. The success of the defence depends, therefore, on the ability of the general, the strength of the fieldworks, the proper disposition of the troops, and the effective use of the artillery.

Permanent defences would begin from the inside and be constructed outward. Geometrical patterns were used to construct bastions along the curtain wall which had interlocking fields of fire against any attacker. In front of the curtain wall, redans would be constructed as outworks, not attached to the bastions or curtain wall. A ditch, either dry or wet, would be constructed in front of the curtain wall and the interlocking bastions. This was designed to impede any infantry assault and would make the curtain wall even taller to the assaulting infantry if they reached the ditch. The ditch might have a palisade in the middle to impede any assault further. Inside the main fortress, a citadel was usually constructed which was the last line refuge for the garrison which they would fall back to if the curtain was breached and the enemy infantry assault was successful.

How the available artillery was employed was critical to the defence of the place:

In the case where one places the cannon at various points in the entrenchments, it will be necessary, as much as possible, that they not get in the way of the infantry, or diminish the execution of their fire. In the entrenchments, as everywhere else, large batteries should not be made, because the enemy can simply avoid them. They often lead to defeat, for they strengthen one point of the line while weakening the rest, which can be all the more dangerous if the number of pieces is very considerable.

Vauban also believed that artillery was critical for the defence of a fortress and should be the main emphasis by the defenders. He also pushed for the development and production of iron fortress pieces, as iron was much less expensive than bronze, but his recommendations were ignored by the Duc de Main, who was the Grand Master of the Artillery during that period.

Finally, it should be stressed that ‘The science of fortification was by no means unknown and uncultivated long before … Vauban.’ The first publication describing a complete system of fortification was written by Errard de Barleduc who served Henry IV, the first Bourbon king of France. Subsequently, the Chevalier Antoine de Ville wrote a treatise of fortification while serving Louis XIII as an engineer. De Ville’s methods were termed ‘the French system’ and he was not only a theorist, but a practitioner. The ‘Dutch system’ was developed by Samuel Marollois, whose writings influenced Maurice of Nassau.

The Count de Pagan was Vauban’s ‘direct ancestor’ in the science of siege warfare and probably served as a model for Vauban. Pagan was both experienced and knowledgeable and his conduct of sieges during the reign of Louis XIII was successful. Pagan’s system was ‘improved upon by Alain Manesson Mallet, and his construction of fortification is … looked upon as the most perfect’ and was little different from Vauban’s first system and was probably the model for it.

Menno, Baron Coehorn, the great Dutch engineer and contemporary of Vauban, has already been mentioned; he was at the same time general of artillery and lieutenant general of infantry in the Dutch service. He was also Director General ‘of all the fortified places belonging to the United Provinces’. Coehorn was noted as being ‘intelligent and sagacious’, as well as ‘thoroughly convinced, that, however expensively the rampart of a town may be constructed, it could not long sustain the shock of heavy ordnance’ and he ‘invented three different systems, by which he throws so many obstacles in the way of a besieging enemy, that, although the place be not in reality rendered impregnable, it is nevertheless so far secured as to make its conquest a business of considerable hazard and expense’. It should also be noted that Coehorn designed his systems to defend Holland, a country that is generally flat and level and so could tailor his fortifications to that one reality. Vauban did not have that luxury. When the two actually faced each other in the attack and defence of places, at the siege of Namur in 1692, Vauban’s system proved to be superior to Coehorn’s.

While fortresses were not the main focus of campaigns during the French Revolutionary and Napoleonic periods, they were still useful in a number of ways. Holding key fortresses in an occupied territory or country was a constant reminder to the population at large that there was a garrison, usually a large one, that could become hostile and a major problem in the event of hostilities.

Occupying and maintaining fortresses in one’s own nation provided a shield or covering force behind which the army could mobilize and take the field. Well-garrisoned and provisioned fortresses supplied with enough artillery could pose a major problem to an invading army, usually so much that forces had to be left behind, or the enemy commander believed that they had to be left behind, to invest the fortress and either nullify it or take it. This could lead to the invading army’s strength being depleted to such a point as to leave it too weak when it finally came up against the defending army.

Fortresses also provided a safe and sheltered environment where recently conscripted units could complete their training before becoming part of the field army. And those garrisons of conscripts could be a reassuring reminder both for the native population and the enemy that the garrison could become a hostile force if provoked. Napoleon used this approach during his campaigns.

Coastal Defences

Coastal defences were necessary for the protection of naval bases, ports, and other facilities deemed essential. The fortifications were usually nothing out of the ordinary and generally followed the patterns developed by inland fortifications other than that they also had to be able to defend themselves against attacking ships if necessary.

One interesting development by the British was the Martello Tower. Built on the coastline, these were round, two-storey masonry structures with a flat roof, upon which would typically be placed one coastal defence piece, either a naval long gun or a carronade. The piece was usually put on a traversing gun carriage that could be pointed in any direction in a full circle. They could be a standalone work, or be coordinated with other defensive measures and they were built in Britain, Canada, and other places in the British Empire. While small and usually armed with only one garrison piece, they were quite innovative, easy to build and man, and if nothing else could provide early warning of a naval or land attack.

Coastal defence ordnance was normally, but not always, of the iron naval type. The gun carriages used with the ordnance could be of several types, including the standard naval gun carriage of the truck type, the traversing carriage, or the older slide carriage. Mortars could also be used in the defence of ports and naval bases.