Stardate 20030405.1907

(Captain's log): Classic raiders would enter a nation, find a village, pillage and loot, and as often as not kill all the men and take children and women back with them as slaves. They'd be on foot, or on horseback; they would wield the sword or club or maybe the bow. We're not talking about very sophisticated warfare here.

The obvious defense against this was to put a wall around the village, often no more than a palisade. The standard early form of this was known as a motte and bailey fortification, but it didn't have to be even that elaborate.

The purpose was to make it so that hostiles on horseback couldn't get in whenever they wanted. If they were impatient, they'd go elsewhere and look for easier prey. If they were determined, they'd lay siege.

The classic siege is a standoff; the attackers cannot readily enter the defended territory, and the defenders are surrounded by the attackers and cannot leave. It's a stalemate which ended when one of the following happens:

The attackers give up and leave.
A relieving force shows up and engages the attackers in battle, defeating them and forcing them to leave.
The attackers run out of supply or lose too many men to disease and leave.
The defenders run out of supply or lose too many men to disease and have to give up.
Someone inside sells out and opens the gate.
A deal is made and the defenders are permitted to march away. (Or think they are, and are killed once the gate is opened.

Of course, there were also flukes and tricks.

As time goes on, you find the defenses becoming ever more elaborate, and surrounding larger and larger areas, and the attackers becoming more numerous and beginning to employ siege weapons. Another way that a siege could end is if the attackers could break a hole in the wall. That's why the palisade was soon replaced by earth or stone walls: wood burns. All it took was one guy with some oil and a torch, and the palisade would burn down.

But when the walls were taller, wider and more strongly built, knocking them down was a real bitch. And siege technology favored the defender until the invention of the gunpowder cannon.

Traditional siege engines such as the trebuchet could fire extremely large masses, but used a high indirect arc and could not really strike the same part of the wall over and over to knock it down. It took repeated blows to eventually weaken the wall, and with a trebuchet that could take months. The big difference with the cannon was that it used a low flat firing arc, and could hit the same area repeatedly. Because of that, large curtain walls ceased to be adequate defenses. Cannons could knock them down in days or weeks.

Fortifications change completely in Europe starting in about the 15th century. Instead of high vertical walls which were easy to hit, the new fortifications were long and sloping, to deflect cannon balls away while taking minimum damage. And they were usually protected by moats. The defenders themselves used cannon, and their cannon were protected and their fire was preregistered. In some cases these defenses became awesomely elaborate.

But as cannon technology improved, with more of them that could fire heavier projectiles and fire more often, it became possible for the besieging force to shoot over the defenses and strike the population inside. Ongoing bombardment like that was thought to eventually weaken the will of the defenders, but usually didn't until the cost in lives was immensely high.

What was needed was really big guns, and you start seeing those at the end of the 19th century. When a gun can fire one ton explosive rounds dozens of times per day, and fire them many miles, it becomes practical to shoot over the defenses of a city to level it, as long as you have enough guns. That compelled the defenders to make sure that their defenses were outside of such artillery range, which actually meant that they weren't really siege defenses at all any more.

In a sense, the Western Front of WWI was one big mutual siege. In the early days, it was mostly the Germans trying to lay siege to all of France, but in particular to Paris. One of the goals for the Germans was to move the lines far enough south so that they could freely bombard Paris with their artillery and thus compel the French to sue for peace, and in fact later in the war they developed a super-gun mounted on a railroad car which actually was able to hit Paris. But it could not fire very often, and it was hugely expensive and they couldn't afford to produce enough such to actually make military difference.

There were sieges in WWII. One of the worst was Leningrad, which was surrounded by the Germans early in the war and shelled for months, with appalling results. And after the Normandy invasion it was part of the German plan that every reasonable port city in France be held strongly; many of them ended up being besieged by American forces. A few critical ones (e.g. Cherbourg) were taken, at very great expense.

But in all of these cases you still have one essential factor: around the city there is an impervious ring of defenders and defenses, facing outwards, who are opposed by a ring of attackers, facing inwards. The attackers can't get in, and the defenders can't get out. If either of those changes, the siege usually ends shortly thereafter.

That's the one unchanging aspect of siege, from the very beginning to modern times: a ring of defenders facing a ring of at