Can I use castles in my story?

13th Century, Metz, France

Used with permission from here

In Aged Chemical Keep I talked about an imaginary, post-apocalyptic future where the survivors huddle in concrete castles, fighting off other tribes that want the security they offer. But is there any place for castles in a world that has modern explosives? Surprisingly, the answer seems to be yes. This post should be helpful to you if you are thinking of creating a world with defensive structures with weaponry more powerful than that of traditional medieval fantasy.

First of all a disclaimer: This post is not rigorously researched. A military historian will be able to find much that is inaccurate here. But my hope is the basic ideas here will be more accurate that the preconceived notions we carry around with us, and get you started thinking along new lines.

Technological changes

First of all, it's important to understand that the history of fortifications is more nuanced than simply castles, followed by their obsolescence. Permanent defensive fortifications were important right the way up to the early twentieth century.[1]

Fort Bourtange

Used with permission from here

The introduction of gunpowder to warfare in Europe in the 14th century - primarily in the form of cannon - was the first major change. But it was entirely possible, even then, to build fortifications that could withstand cannon fire. In the mid 15th century, a new form of fortification was seen - the Star Fort, pictured right.

This introduced a number of new ideas, but principal to its layout is the idea of overlapping fields of fire - each of those pointed bastions would have had cannons on either side that could cover the next bastion over, as well as the flat wall in between. Additionally, there are large shallow ditches that slow attacking troops and which can also be fired on from the bastions.

The next big technological change was the introduction of explosive shells. These required a different kind of fortification, with a lower profile to make them hard to hit with artillery, and massive earth ramparts that could absorb the explosive damage. These fortifications continued in use, with modifications, until the early 20th century.

The changing role of fortifications

However, what is more interesting than the architecture of these forts is the way in which they were used. Increasingly, cities were no longer constructed with walls around them and a keep in the centre. Instead, forts were placed at strategic locations near cities, where they could fire upon approaching armies. Over several centuries, forts became much more about secure places for troops to fall back to, places to mount raids and harass armies from, secure stores of supplies, and so on.

Ohrid, Macedonia

Used with permission from here

As I understand it, the chief reason for is a change in societal structure, through population growth and a changing conception about the nature of nations. Gone were the days when a city state could be surrounded by secure walls, because cities grew too quickly. The new kinds of fortification, such as the star fort, were very expensive to build and when populations grew they couldn't enclose the new city. More than that, increasingly wars were not between neighbouring cities, but between larger entities, such as today's nations. When your populace is spread throughout a whole country, the investment in permanent fortifications to provide good coverage would be huge - but the enemy only needs one army to attack anywhere.

This is even more true in the latter half of the 20th century - with planes, long range weaponry, and very mobile troops your enemy can strike anywhere. If they invest their resources in offensive capabilities and you in defensive capabilities, you will have to spend orders of magnitudes more to defend even most of your important locations, whereas their single strike force can be anywhere. And so we come to modern warfare, which is largely about temporary defences, and highly mobile forces.

So when are forts useful?

So what about our fantasy settings? Is there a time when forts are conceivably useful? I think the key question is the cost of the fortification relative to how long it will be useful for. The more advanced the weaponry, the more stable and localized a community has to be to make it worth them building a fortification.

In the Aged Chemical Keep scenario, I think the fortifications work really well. This is because the tribes are small - I imagine 20 to 200 people - and they are not growing fast. So it is easy to protect everything and everyone they care about by retreating to a single one of these concrete forts. 

Aged chemical keep

My own modification of this photo

I think the post-apocalyptic setting helps here, because attacking forces will also be small, and while there may be extremely powerful weaponry around, it is not consistently available - many tribes will have access mostly to anti-personnel weaponry, and maybe one or two portable rocket launchers with limited ammunition. But the threat of a surviving tank, plane, or other high-explosive delivery mechanism gives the setting tension - one day the fort could fail them.

Of course, the forts are also left over from another period, which helps, as the characters didn't have to build them. Finally, the hostile nature of the outside world gives an additional reason to huddle inside.

So any time you have localized communities - medieval seats of nobility surrounded by a few miles of farm land, mining outposts on snowy planets (ignoring attacks from space), post-apocalyptic tribes, monk-like guardians of ancient and immovable wellsprings of power - you can consider borrowing the imagery of castles and fortifications for your story.

A final thought

I think it is much harder to reconcile castles with high fantasy where magic is common, as they frequently are used, than with many contemporary technology settings. With magic, you potentially have weaponry as powerful as anything in the modern world at the fingertips of a single wizard. With magic, attackers may be able to transport themselves behind enemy lines or pass through walls. Authors who intend to introduce magic as a common force into the world need to think hard about the impact this has on economy, society, and warfare if world consistency is important.

Other sources:

• Maginot Line or Fort Apache? Using forts to Shape the Counterinsurgency Battlefield
• Lime Point Military Reservation and Fort Baker: Battery Cavallo
• The Decline of Medieval Castles

Search keywords: Why have castles declined? What made castles and other fortifications obsolete? Castles in post-apocalyptic settings. Castles in sci-fi settings. Castles in fantasy settings.