Late Period Fortification

Transcription

1 Late Period Fortification Much of this article is edited from one by Barry L. Siler found on the following site. This great site has animated or interactive illustrations. Development of the Star Fort Successful Defense Against Artillery: Pisa, 1500 As the new offensive force of artillery displayed its power in Italy in 1494, the first effective defense against that artillery was demonstrated also in Italy a mere six years later. This was the wall as a low-profile rampart with a ditch in front. In 1500, Pisa broke with Florence, which then asked for and received aid from the French to bring the upstart city of Pisa back under Florentine control. A combined force of French and Florentines laid siege to Pisa. In short order the French artillery began hammering the Pisan wall. But! The Pisans, by then wise to the power of cannon against the fragility of their vertical stoneware, fashioned an earthen rampart, with ditch before it, behind (but not part of) the particular wall being battered by French cannon - think of a defense within a defense. After the wall was soon breached, French foot surged through the opening. They were met with::: Another barrier! With feisty Pisans atop and behind it. The enthusiasm the French had for the assault dropped lower than the ditch in front of them, and soon they and their Florentine clients abandoned the siege. (Only a blockade in 1509 compelled Pisa to bow again before the feet of Florence.) What the Pisans made was referred to as a Retirata. The Venetians expanded on the retirata for their defenses at Padua in A retirata was a 'make-do' retrofit. After Pisa and Padua, the basic concept of its rampart and ditch was put to use in the development of new defenses to replace the old. Low, thick walls, with a base considerably wider than the wall's height, could not topple over. With an interior of fill, usually earth and/or rock, such a wall could absorb one cannonball after another (in the days before exploding shot was fired from cannons). Low, thick walls became the fundamental strength of a new type of defensive design.

2 Rampart and Ditch Cannon drove fortification development. Cannon forced the defensive mind to adopt and refine in a very few years a type of fortification that was visually less impressive than stone vertical walls but far more resilient to the new force. The very first of these types of fortifications employed two fundamental elements: 1. a Rampart, sloped in front and low in profile, and wide enough at its top to permit men and cannon to be deployed there; 2. a Ditch or Moat in front to hamper advancing attackers, any delay or even slowdown thereby exposing them to defensive fire. In cross section, unlike the stone curtain wall, the rampart was low and squat, wider than tall, with a sloped front. It did not defy gravity - it could not topple over. The first ones were made of earth with some reinforced with stone and wood. Cannonballs striking such a thick, earthen slope would merely bury themselves into it without breaking it down - gravity was no help. Keep in mind that in those days, cannonballs were solid, not packed with powder to detonate soon after impact. Their destructive power was in the punch. Being able to absorb them, low, sloped, thick walls became the fundamental strength of a new type of defensive design - but they had to be thick enough to withstand hits from a 24-pounder cannon. The ramparts of an artillery fort were not as high as the walls of medieval times when the higher the wall, the Compare the high curtain wall to the low, sloped rampart. Which is more likely to collapse? better to fend off attackers with siege towers and ladders. For the artillery fort, artillery and small arms fire kept attackers sufficiently far from the ramparts. If defenders became so weakened and their firepower so depleted that attackers could reach the base of the ramparts, high walls would not stop them at that point. The ditch in front of the rampart was conveniently created by shoveling out dirt to build the rampart. The ditch made the rampart higher from its base plus created a pit that slowed attackers and tended to entrap them. Thus, a secondary feature of the rampart defense became integral to its stopping any charge.

3 The Ditch Becomes A Moat Water in a ditch slowed attackers more than a ditch of dry ground (try running through water even only two feet deep with a mud bottom). A ditch could be filled with water if there was a convenient source like a stream or if the water table was high enough, which it usually was in some provinces of the Lowlands, such as Holland and Zeeland. Unfortunately for defenders of forts in northern locales like England, the Netherlands and the Baltic states, bitter weather in winter could put a coat of ice across the top of a moat sufficient to support attacking foot - and this period was well within the Little Ice Age. A rampart with a ditch/moat in front was not sufficient to stop an assault. A third element was needed to cover these two with shot. That third element of the trace or ground plan was so designed that around a fortification's perimeter there would be no spot left untouched by defensive fire - to make a play on words, no Dead Ground so there would be only a killing ground. The Basic Bastion Defenders needed to cover all ground around their fortification no spot to be left unexposed to defensive fire. That need was fulfilled with the addition of the Bastion, which from above resembled big, angular knobs, usually at corners and angles of fortifications. Soon after 1500, the bastion, the third key element in the design of the new style of fortification, was married to the rampart and ditch concept to form an artillery fort design that rendered any attacker vulnerable and killable. With bastions, defenders could have permanent flanks to jut into any attacking force like peninsulae into the turbulent sea. Francesco Laparelli in the 1560 s stated: Without flanks, it is impossible to defend a place against an army with artillery. (Laparelli designed the fortress and city of Valletta, Malta)

4 From their extended vantage point, defenders could view any and every part in front of and around the artillery fort and spot sooner than before any sneak attack. Defenders could comfortably take a clear shot at any would-be attacker. Straight sides along the two straight faces of a properly designed bastion eliminated any blind spots. If any soldier approached the ditch, stood in front of the ditch, tried to cross the ditch, or scrambled up a rampart, he could be put in the grave by defensive fire from the bastions. As static flanks for defenders, bastions could extend farther out than towers. Like comparing ramparts to curtain walls, bastions were thick and squat compared to castle towers. They couldn t fall down and were built broad enough to hold many defenders. The elegant tower could not match the chunky bastion for resilience against cannon and the increased size of besieging armies Caliban succeeded Arial on the stage of war. The combination of rampart, ditch and bastion was conceived, developed and honed in Italy during the first half of the 16th century and, when other areas of Europe adopted the concept, it was dubbed the Trace Italienne, Italian for "Italian Design." (Incidentally, within Italy, the concept was usually referred to as "Alla Moderna," meaning "of the modern way.") Model of the basic bastion for an earthen fort. Cannon emplacements have been added. To give a sense of scale, one of the emplacements has a cannon with a crew member there, and that dark object near the top of the image is a wagon drawn by a team of two horses. What Makes a Bastion While the fire from one cannon may have an effect, fire from two on the same attacker would have a improved chance of scoring hits. From three - or four - even better! With bastions sticking out from the core of the fort, cannon mounted on them could not only lay down overlapping fields of fire but also intersecting fields of fire from two neighboring bastions. The enemy could be caught in a crossfire. Plus, should a cannon or two be silenced, defenders still could cover the field before them. The successful bastion not only protected itself from every place an attacker could strike it but also its adjoining ramparts and - very important - neighboring bastions. The mutual support of bastions, with one being able to lay down protective fire for another, was why this concept became so successful and so widely adopted. What an observer immediately notices is the arrowhead-like shape of the bastion, with straight sides, not curved. Straight sides allowed fire to be directed by defenders along any portion of its sides and out onto the ditch and ground beyond; there was nothing sticking out to interfere with lines of fire, no places to shield attackers. If attackers at the base of a wall or tower could

5 not be reached by defensive fire, then they could be free to tunnel under to undermine or set explosives. As mentioned earlier, the round tower of the medieval castle/fort did leave blind spots for defensive fire. But a bastion with incorrectly angled sides also afforded protection for attackers. One bastion protected other bastions at either side. Atop those short faces, defenders could mount cannon to blow away any attackers on the walls or the side of the adjacent bastion. If the bastions were within 250 yards / 220 meters of each other, musket fire could also be brought to bear on anyone assaulting an adjacent bastion; in the Netherlands, bastions were usually set within 250 yards of each other specifically to make use of muskets. These angled bastions set at intervals along the walls offered an effective and deadly system of mutually supporting fields of fire. Some of the rampart walls face each other and would have the defender's cannons firing into their own ramparts. Did they really do that? Yes. Not commonly with cannonballs, however. Preferred was canister shot. Any piece in canister shot was not large enough to damage the defensive works but all together certainly sufficient to, um, shred groups of attackers; in modern parlance, it was "antipersonnel." Aware of the potential of canister shot, attackers were hesitant to swarm up the sides of ramparts unless the defender's cannons were already silenced. Between the angled planes of the bastion and the ramparted walls, there were narrow faces set usually 90 degrees to the walls, especially for earthen bastions constructed in the Netherlands. These were frequently referred to as Flanks. When the bastion was built of masonry, these faces could be inset into the base of the bastion. Inset or not, that little space afforded defenders virtual immunity from enemy fire unless the enemy got very close to the fort. Ramparts set LESS than 90 degrees to one another proved to have the better ratio of shooting lines to adjacent bastions. A common bastion-to-bastion angle was 72 degrees.

6 What Shot Out of Cannons Cannonball Solid cast iron balls were shot at anything. These did not explode. The technology for such wasn't there - yet. Nevertheless, even against massed infantry, these balls could be devastating. Fired to angle horizontally through a formation, a single ball could chop a bloody swath*; it could even be made to skip along the ground through a group like a flat stone across water, amputating and disemboweling as it skipped. Canister Shot - Small Ball Of somewhat smaller diameter than the cannonball, such shot was usually round balls placed inside a canister, which was often metal but in a pinch could have been something else like leather. The projectiles could be pre-made specifically for this purpose and were usually larger than musket balls. Should the balls be packed inside a cloth bag instead of a can, the collection was dubbed Grape Shot, for it resembled a bunch of grapes. Canister Shot - Assorted Metal Objects An alternate to small-diameter metal balls for canister shot was whatever came conveniently to hand, such as scrap metal, nails, links of chain, etc. The canister acted as a sleeve to carry this aggregate along inside the barrel during firing. Due to the lack of any aerodynamics whatsoever to these sorts of projectiles, likely their range was not as far reaching as that of ball. When a breach was made in the defenses of Siena in 1555, the defending commander, Blaise de Monluc, had four or five heavy cannon, he wrote, "each loaded with great chains, nails and pieces of iron," fire at attackers stepping into that breach. Hail Shot Hail shot was most often musket balls in a small cloth bag, the opening tied off. The bags were fist-sized or smaller and fired from small-caliber cannon like a falconet. Into any group of attackers, the shot would rip like hail, as its namesake would on a sprouting garden.

7 The Shape of a Fort For the best angles to shoot along each bastion face as well as the walls, the most practical overall shape to the new artillery fort became a pentagon, with sturdy bastions protruding from each corner of the pentagon. Each of the five sides (and usually likewise with the five bastions) was the same size. From this shape comes the term used for this design: Star Fort. Some small forts were laid out as rectangles and a few were even triangular in design. The angling on the bastion fronts varied, with fortresses in the Low Countries having sharper angles and usually set within 250 yards / 220 meters of each other to have one within musket range of the other. Bourtange, a Dutch Star Fort from 1580 Such clean, geometric architecture could only be practically applied to new defenses set out on land not already occupied with a city or town. Established towns and cities required the new Trace Italienne to bring their defenses out of the Middle Ages. But to retrofit what was already there ruled out simple, even geometry.

8 Face it! Was Earth the Best Material for Building a Fort? For a readily available construction material, it was earth. It could be shoveled out to make the ditch and heaped to create the ramparts. Even if one had a construction crew of unskilled labor, all anyone had to know was how to wield a shovel, basket and wheelbarrow. Plus, construction was as fast as that earth could be dug, hauled and dumped. Such earthen forts popped up all around the Low Countries after But an earthen fort had two serious drawbacks: Earthen forts eroded to uselessness in as few as four years. 1. The finished fort eroded quickly. Unless continually maintained, erosion and settling of the heaped earth rendered it useless in a mere four to ten years. 2. The angle of the front of the rampart of an earthen fort could not be any steeper than what mountaineers and geologists today refer to as the "angle of repose," that angle at which the material is at rest - but barely. Any steeper and it slides down. An addition could be made to fort construction to alleviate those two problems: masonry. To correct #1, ramparts and bastions faced and anchored with stone or brick - masonry - held up much longer to the elements. Maintenance was reduced from an ongoing challenge to fixing the occasional nuisance. For #2, earthen forts, the "angle of repose" was often in the neighborhood of 45 degrees - or less. The serious problem with that angle was that it was not sufficiently steep to prevent attackers from stepping right up the wall all the way to the top. With masonry to hold the wallwork in place, facings could be steeper than any man could leg himself up. Angles could be 60 degrees or steeper. Yet the thickness of the walls was enough that cannon could not make them topple (although the masonry could be shattered to slide down). Revetment was the name given to a facing of masonry.

9 Bastions With 'Ears' Orillons, Italian for "ears," could be added to masonry forts because firm walls of masonry could physically support such architectural features on the bastion. You can see where the name comes from by the way they stick out from the sides of the bastion. Orillons were usually constructed at both sides of a bastion, where the flanks met the ramparts. This feature allowed the cannons for those positions to be set back into the bastion, with a curtain of masonry jutting out to help shield the cannon and crew from besieger's fire. While the enemy could pick off other cannon arrayed along the outer sides of the bastions, those cannon tucked back behind the protecting orillons were out of sight from the front and hence out of the line of fire. They were tough nuts to crack. Orillons came in two styles: squared-off end as seen in the model above or a rounded end as seen at the left. Each style was a good as the other for protection, and which was employed was a matter of taste for the architect or engineer. Rounded versions tended to be most frequently seen on Italian forts. To further protect the cannon and its crew behind an orillon, the platform for that gun could be lower down in the bastion than the gun platforms elsewhere on the bastion. This is illustrated in the model below.

10 Defenses outside the wall The term 'body of a place' was used to refer to the 'base fort' or what's within the innermost ditch because assorted fortifications integral to the defense were constructed beyond the ditch. It was these the besiegers first encountered, hammered and had to take, thereby suffering casualties and delays - and any delay jacked up the cost to the besiegers in supplies and attrition in the ranks - and any delay provided that much more time for a field army on the side of the defenders to march in. Plus, these outworks provided bases from which defenders could make sorties, anything from reconnaissance to counterattacks. The first defensive feature outside the ditch was a triangular shaped structure, the Ravelin, that stood in front of the bridge and gate to defend the way for supply and communication. On the far side of the bridge, the lightest sort of defending structure was a simple wooden gate and a few meters of wooden fencing to both sides. While this may have held off bandits checking for an opportunity, such was too puny to stop an army. Something more in keeping with the fort's strength was needed to be in front of the bridge. That something was the ravelin. The ravelin was beyond the ditch and in line with the gate and bridge. In appearance, a ravelin was like the front part of a bastion: it had two walls as salients that came together at the outer end to make a point. Often, the ravelin was more pointed than the bastions nearby. Before 1650, it was usually open at the end closest to the base fort and was lower than the ramparts it stood before (which enabled defenders in the base fort to fire down into the ravelin should the enemy be overrunning it). Like the base fort, a ravelin could have had a ditch along the outside of the two walls. A synonym occasionally used for ravelin was "demi-lune," especially in French references, and may have been conceived by some earthwork ravelins having a rounded front instead of a point. The first ravelin was built in 1497, at Sarzanello, and it was masonry. Picturesquely weathered, it remains standing today. The road from the bridge turned to go behind the ravelin, usually paralleling the ditch until beyond the ravelin. Engineers often extended this parallel farther than the ravelin in order to leave vulnerable to fire an enemy bringing up anything that required a road.

11 The ravelin is that chevron-shaped structure in the middle, in front of the bridge and gate. As with the bastions, it could be a platform for cannon. In this example, the ravelin was built entirely of earth but could have instead been made with masonry like the fort behind. Engineers and military experts realized by the end of the 16th century that a large ravelin provided increased flanking fire to help protect bastions at either side of it. Defenses were then supplemented with ravelins spaced in conjunction with bastions along entire sections of the base fort, sometimes completely around it. Access to these ravelins was from the covered way (to be discussed later). Then, before besiegers could make the final assault on the base fort, the 'body of a place,' they had to get past at least one of the ravelins. That meant bombarding it, then taking it, consuming men, material and time. Supplementing the Ravelin In addition to ravelins, outer defenses were sometimes augmented with what were essentially expansions on the purpose of the ravelin: Hornworks and Crownworks. The shape drawn on the plans suggested those names, as you can see in the illustration at the right. For most artillery forts, these outerworks were lower than the base fort so that fire from the fort itself would pass over them. Some engineers were cautioned, though, about building too much for outerworks because such could become shelters for attackers after being taken.

12 In the 1570's, the Dutch heaped up earthen ravelins and detached bastions in front of old town walls, following what the French Huguenots had done in the religious/civil wars in France of that time. Shortly thereafter, the Dutch expanded on the theme with angles thrusting out toward the intended enemy. Such structures were sited so as to command vulnerable ground, providing critical flanking fire. The Dutch patterns were quickly adopted by others. In addition, fortifications were put up outside the town or city, some of which were essentially forts. As the 17th century progressed, outerworks were elaborated upon, with moats around them and outerworks on outerworks. In their complexity, they became, um, quite Baroque. Covered Way & Glacis While digging the ditch, workers could carve into the top outside edge all around the perimeter a shelf deep enough for a man to stand upright. A short step would also be shaped to enable that man to make himself high enough to peek over the edge and, if a musketeer, take a shot or two at prowling enemy. The protected shelf with little step inside was the Covered Way. Completely surrounding the ditch, the covered way enabled outside defenders to reposition themselves to one side or the other in response to enemy pressure. The covered way was so vital to the overall defense of the artillery fort that a common saying in some 17th century armies was: "Covered way lost, everything lost!" Another way to judge the importance of this feature and how it was employed was its synonym: "covert way." The concept of the covered way was originated in 1556 by an artillery expert, Niccolo Tartaglia, as a place for stationing some infantry before the walls. This worked so well that in construction of later forts the covered way was widened in order to hold more troops. They became as wide as six to seven meters.

13 Sloping at a slight angle out from the covered way was the Glacis. This featureless plain. offered an exposed field to be swept by defensive fire. More important, it raised the ground in front of the fort's walls to protect the base from enemy artillery. The glacis "lowered" the profile of the fort itself, rendering it less exposed. Gabions, Fascines, and Bales of Wool Protection for infantry and artillery was handily provided with gabions, fascines and bales of wool. Portable, these were made and deployed in little time wherever the enemy placed his fire. These supplemented fixed defenses, say, a row of gabions atop a parapet or in front of the covered way. They were also thrown up to create temporary works. Although included in this section, these items were as much used (and often more so) by the attackers to shield their trenches as they dug toward the fort. Basically, the three functioned to absorb small arms fire, canister shot, and perhaps the small-bore cannonball that was mostly spent in its trajectory. But something like a 24- pounder could have turned a gabion into a shower of dirt and broken rock.

14 Gabions were woven in various sizes. Usually, they were open at both ends, and the vertical rods extended a several inches from one of the ends and were sharpened to anchor in the ground. Set on that end, the "basket" was filled with dirt and rocks, which could have been right out of the trench being constructed. Once filled, they became immobile but were sturdy, affording protection - as long as one did not stand in any gap between two. For that contingency, gabions were occasionally arranged in two closely spaced rows, alternating with one another. They were also stacked one atop another, if the basket makers were producing short ones. No period illustration shows, however, more than two tiers of gabions. The modern-day replacement is the sandbag. Instead of a second tier of gabions, sticks and wood tied together in bundles could be laid atop gabions. These were Fascines and could be made quickly by any soldier, unlike gabions that were woven by those with basketmaking skills. A portability drawback to gabions was they became immobile once filled (unless unfilled), whereas fascines could be picked up to be moved to another site. Of course, fascines were also used by themselves, sometimes stacked several deep or even racked on their ends. Fascines typically were one to two meters long, but some, called saucissions or sausages, were as long as five meters, used atop parapets. Wool bales at first seem a curious sort of shield. Thinking beyond Little Bo Peep and cuddly lambs, a fat bundle of wool densely packed would absorb a musket ball as well as a gabion. Furthermore, in some areas wool bales could have been easily had. Wool production, especially in the 17th century, was an expanding industry and wool actively traded. Some towns could have had sheds and warehouses stacked with bales. One wonders, though, about the market value of any wool bale after it was shot up in a siege.