Friday, September 5, 2008

Siegecraft - The Defenders

The full-blown Star-Fort layout

The invention of cannon basically caused two changes from the classic medieval fortress. The first was that high walls built above ground could be quickly knocked down from a distance, making them useless. Instead, these walls were cleverly swapped for a ‘walled ditch’ idea, where attackers from a distance would only be able to see the very top of a wall (from which the defenders could fire on them) and would have to go to the prolonged and dangerous effort of working their cannons up to the edge of the ditch, right under the noses of the defenders, before they could fire on the wall and knock a breach in it.

The second change caused by artillery was from the defenders’ perspective. Firing a cannon out on a mass of attacking enemy troops was all very well and good, but if a breach had been knocked in the wall then this was the one point of the fort where you couldn’t put a cannon. What was really needed was a way for other cannons on either side of the breach to be able to fire across at it, sending cannonballs hurtling down the ditch in parallel to the fortress walls so that attackers would be cut down in rows. The whole thing would begin to resemble a bowling ball thrown down a lane at a bunch of skittles.

The answer was a bastion – a kind of projection out from the main wall of the fortress, which would allow guns to be sited in it’s sides, facing along the length of the main wall. By shaping the front as a wedge, the front of each bastion could also be covered, producing the following layout.

Plan views to give the evolution step-by-step:
Top - A wall. (Yes, I know it's that simple!)
Middle - Bastions, plus firing lines between them, but with their fronts unprotected
Bottom - The bastion fronts are angled, allowing protecting fire all along the wall

When done to enclose a circular area, it’s the classic ‘star’ shape on plan, and it means every inch of wall is protected by flanking fire – each wall is covered by it’s neighbouring bastions, and each bastion is in turn covered by its’ two adjacent bastions.

The more defensive ‘projections’ like these bastions there are, the more lengthy and difficult the siege. With this in mind, it was common to put little mini-forts, separate from the main works, further out in the ditch. Most common was the use of a diamond-shaped island called a Ravelin, which would sit in front of the wall between each bastion. That’s the level I’m stopping at, but historically the system led to a blizzard of outworks of various names like Lunettes, Tenailles, Hornworks, etc. which could basically be repeated as often as space, time and money permitted.

Plan View, with Labels
Bastion lines of fire down the ditch

Ravelin & Bastion lines of fire down the Covered Way

The last touch was the outer edge of the ditch, which was given a protective infantry position known as the covered way. Basically it was a kind of open-backed trench, which allowed infantry to fire on the approaching besiegers and guaranteed that the attackers were going to have to carry out a costly assault if they wanted to clear the edge of the ditch and get guns to it.

A section, looking sideways through the defences. From left to right: the wall & bastion with cannons on top; the ditch; Infantry in the Covered Way; the Glacis (a sloped approach)

The attackers’ experience if he tried to progress through these works would be a daunting one. First, a run up the gently sloping Glacis (a clear no-man’s-land, within musket range, and kept barren of all cover) with the enemy infantry in the covered way firing as you came, and the cannons in the fort firing over their heads and down the slope at you. If you made it to the Covered Way and stormed it, things didn’t improve – it was open-backed, with no cover from the defenders’ guns, making it a gigantic ‘bullet-trap.’ Now it wasn’t just the cannon on the wall in front of you, but cannons to the side, in a ravelin, firing lengthwise down the covered way and sweeping away ranks at a time. Storming the ravelin would be no good, as this just left you in another bullet-trap unconnected to the main fortress. If you clambered down into the ditch, you then had cannons in bastions to your left and right sweeping it with fire, all carefully calculated for maximum destruction. Oh, and the wall in front of you is still probably mostly intact except for the very top, meaning that it’s impossible to go forward and all the effort’s been wasted…

That runs through a fair bit of the defensive theory, so next post will be from the attackers’ perspective, explaining how this system would be overcome by the besiegers. Hope you enjoy!

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