Armies clashing on hilly terrain.

Writing fantasy battles can seem overwhelming when you’re first starting out. There are so many factors at play, from what type of armor everyone is wearing to how orders are issued across the battlefield. Where do you even start? Fortunately, you don’t usually need to portray the battle itself in extreme detail. Not only do readers’ eyes tend to glaze over when they’re hit with too much description, but the more detail you include, the greater the chance of getting something wrong.

Instead, most stories are best served by focusing on a few specific details and then leaving the rest as an abstraction for the reader’s imagination. This way the reader is firmly anchored in the action without being overwhelmed. Which details you put under the spotlight depend on the story, but terrain is always a good option. Not only can terrain have a huge impact on a battle’s outcome, but focusing on it gives you an excuse to describe the environment, further immersing the reader in your scene. Let’s take a look at a few of the ways terrain can impact your story.

1. Swamps Exhaust Armies

A painting of Seminole soldiers preparing to ambush the US Army.

Fighting in swamps is a nightmare. Moisture gets into everything* and ruins valuable equipment, from bowstrings to gunpowder. Large armies are difficult to coordinate in a swamp, and dense foliage offers many places to hide. In swamp country, a small force can hold off a much larger enemy for a long time, something the US Army learned firsthand from the Seminoles in the early 1800s.

But even just moving through a swamp can devastate an army. The wet ground makes for a very slow pace, which means more time in the field eating up the army’s supplies and that’s assuming they don’t need to get somewhere in a hurry. Compounding the problem, heavy equipment like supply wagons can easily get stuck in the mud, or even sink completely. This is even worse if the army has artillery with it, as cannons are often the first thing to slide into the muck.

Then of course there’s the cost to soldiers. Swarms of insects bite every human they can find, spreading disease and ruining morale. Food rots from all the humidity, and it’s difficult to stay clean. All of this makes swamps excellent for defense, to the point that Ravenna was once chosen as capital of the Western Roman Empire because the only land approaches were through dense swamps. That made it extremely difficult to attack, and it remained vital long after the collapse of Western Rome in 476.

The obvious use of swamps in your story is as somewhere for your plucky band of rebels to hide. The swamp protects them from the bad guys, but then the heroes have to deal with finding food, withstanding illness, and wrestling gators. Alternatively, your story could feature a general who needs to move their soldiers through swampy terrain in time to save a city from falling to the enemy, in which case time and the swamp are allied together as the true antagonists.

2. Uneven Ground Breaks Up Formations

A painting of American soldiers marching up hill around rocks at the Battle of Chapultepec.

In a modern setting, having soldiers stand shoulder to shoulder in large groups would be pretty silly because of the all the bombs, missiles, and grenades, but that’s not the case in most fantasy stories. Formations will be a big deal in any setting where the lion’s share of combat is still carried out face to face, as they protect soldiers from harm and allow them to devastate less-organized forces.

In Western culture, the most well-known formation is probably the Greek phalanx, and with good reason. In various incarnations, the phalanx was by far the most powerful military unit across the Classical Mediterranean and as far east as Alexander’s conquests took him. In close combat, the phalanx was nearly impervious, breaking up lesser formations with ease.

But the phalanx, along with most tight-backed formations, had a weakness: rough terrain. If a phalanx’s soldiers couldn’t stand shoulder to shoulder because of natural obstacles, it created openings for an enemy to exploit. And, oh boy, were the Romans happy to do some exploiting. Whenever a phalanx was disrupted, the more flexible Roman manipular legions would close in and cut the Greeks to ribbons with their short swords.

This strategy was particularly effective against later iterations of the phalanx because they used a 20-foot-long pike as their main weapon. Once an enemy closed in, the pike was nearly useless. However, uneven ground can have a similar effect on any rigid formation, as they all depend on soldiers bunching up for better defense.

This dynamic is a great way for your unorganized army of loose-cannon heroes to defeat the better-disciplined evil empire. Sure, the empire’s soldiers are drilled with perfect discipline and brutal efficiency, but your heroes have heart – and also advantageous terrain. If you want a story that explores the other side of this equation, uneven ground can be a great way for your arrogant imperial protagonist to get some spinach, as their shining legions are cut to pieces by “barbarians.”

3. Currents Hamper Ships

A painting of the Ottoman victory at Preveza.

Hold on a second, water doesn’t even have terrain, does it? It’s all flat and wet – that’s what it’s known for! Well, it turns out that currents are essentially underwater terrain, and they can have just as big an impact on the battlefield as mountains or swamps. Combine them with rocks, shoals, and other submerged hazards, and you’ve got the potential to change the entire course of a battle.

Humans have been aware of this for a long time, and they’ve planned accordingly. One of the many reasons Constantinople made such a good capital for the Eastern Roman Empire was that the currents just offshore were extremely treacherous for ships of the time. Sailors unfamiliar with Constantinople’s waters were likely to run their ships aground, and so attack by sea was difficult.*

In battles between ships, currents are even more important. When those ships depend on sails or rowing for propulsion, the force of a strong current really makes a difference. Whichever side is sailing with the current will have big advantages in maneuverability, allowing them to attack when and where they please. If an admiral is skilled enough, they might even maneuver their foe into smashing against one of those underwater hazards we talked about earlier.

How you use this in your story depends on context. If you need a reason for underdogs to defeat their more-powerful enemies at sea, then superior knowledge of currents is a great option. Your heroes can be totally outgunned and still win the day if they’re used to sailing these waters and the other side isn’t. Alternatively, you can up the tension by having your heroes sail into unknown waters, always at risk of being swept onto the rocks.

4. Slopes Impede Cavalry

A painting of the rough terrain at the battle of Somosierra.

It’s hard to overstate how important the horse was in historical warfare. Mounted soldiers have far greater mobility on the battlefield,* allowing them to exploit enemy weaknesses. Under the right circumstances, a cavalry charge can devastate enemy formations. Even more brutally, cavalry can ride down fleeing enemies so they don’t escape to fight another day. Then you have horse archers, which can rain arrows down on the enemy and retreat before they take any hits themselves.

But all of these advantages require relatively flat, open ground. Horses are not good climbers, and a serious slope will stop them in their tracks, whether it’s uphill or downhill. At the same time, horses are notably larger than humans, and so they have a harder time maneuvering around densely packed obstacles like trees. A cavalry army trying to fight under these conditions will find its mighty steeds quickly transformed into inconveniently large pets who eat a lot of oats.

That was the situation the Spanish found themselves in during the Great Inca Rebellion. An Inca general named Quiso realized his forces simply didn’t have the technology to fight armored Spanish cavalry head on, so instead he lured his enemy into the mountains where the extra mobility of a horse was useless. Once the Spanish were trapped and unable to maneuver, Quiso’s soldiers dropped boulders down on them. The tactic was devastating, and it only failed when Quiso was ordered by his emperor to attack a Spanish city on level ground.

If your heroes depend on horses, then steep terrain is a great way to make things harder for them, especially if the enemy doesn’t have that problem. Perhaps the villains have access to a steampunk tank that climbs up mountains with ease, while your heroes are now stuck on foot. But your heroes can also use slopes to their advantage, especially if they’re mostly on foot facing an army of plate-clad knights.

5. Soldiers Can Build Their Own Terrain

An old illustration of a Hussite war wagon.

Until now we’ve been looking at natural terrain features, but that’s not the only way to shape a battlefield. Instead, soldiers can make those alterations themselves. This is something that rarely seems to come up in fiction, even though it was a really important aspect of historical warfare. Stories have plenty of castles and great walls, but engineering projects on the battlefield itself rarely grace either page or screen.

The first artificial terrain feature to familiarize yourself with is the ditch. Historical commanders absolutely loved digging ditches. Sometimes these ditches were covered up and used as a Scooby Doo–style trap, only with much higher body counts. This is what happened to the Sassanid Persians at the Battle of Gurgan,* when the Hephthalites feigned retreat across a hidden ditch and presumably played hilarious music as the pursuing Persians tumbled in.

A more common use of ditches was to shape the battlefield. If a commander felt their center was vulnerable, they might have a ditch dug there so the fight would be channeled into the flanks. Byzantine general Belisarius famously used this tactic, also against the Persians, at the Battle of Dara.* Makeshift walls were built for the same reason. They either aided in defense or forced the enemy to attack somewhere else along the line.

Artificial terrain was generally used by the defender since the enemy had to come to them, but in sieges the reverse could happen. To ensure absolutely nothing got in or out, the attackers would often build a wall completely encircling the besieged stronghold. The Romans were famous for this, as their legions were mobile construction crews as much as soldiers.

How you use artificial terrain is dependent on the mood you want for your story. If you’re going for a desperate last stand, then your defending heroes might take a page from Belisarius’s book and use a ditch or wall to stave off a more powerful enemy. If you want your heroes to be more active, maybe they need to break out of a besieged city, and to do that they must first get over the attacker’s shiny new wall.

This list presents just a few of the ways terrain can affect a battle. If it fits your story, go into more depth. You could write about how the prevailing winds blew smoke or dust into one army’s eyes, or how a single muddy patch on the field broke up a charge at just the right moment. But remember, most stories don’t need that level of detail. It’s okay if you’re not an expert; you only need to provide enough context for the readers to imagine what’s going on for themselves.

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