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World: The world is 1/4th the diameter of Earth, and there are 2 continents + the poles, like our poles. Esia, 25% of the size of real-life Asia, and Aurope, 25% of the size of real-life Europe. Their is less ocean proportionally than our world and the gravity is Earth-like with the planet inhabited by humans.

Kingdom X, back from last question, has constructed the largest series of fortifications ever. Consider Asia as an oval 2000km by 1000km (tell me if my land sizes are unrealistic). Kingdom X is bordered by the ocean, and has a natural mountain range (considered impassable) with a continuous gap around 700km long.

This Gap is 200km and is a large seath of flat terrain. It is uncolonized similar to the Korean DMZ due to border disputes. There are several trading towns on either side of the gap including Kingdom Y, but the Advent of railroads means that their population is small and inufficent to stage an army from.

The population of Kingdom X is 30 million people, with a defense millita of around 20,000 (don't want the peasants to revolt now). Around 20% of the population are magicians. Kingdom X needs to defend against 50,000 people once every 6 months and 100,000 every few years. Assume that these armies only start once the defense sufficiently impedes smaller armies.

Magicians in this world replace cannons and guns (simply no need). Training time is around 4 years from childhood, and fireballs 1 feet in diameter can be thrown once a minute for an hour, or more per minute for less total time. Resting time is about a day. Magicians can also shoot lightning, but I don't forsee that chaning much. Calvary and chariots are widespread, and so are crossbows.

Technology is still early-steam with feudal elements, including steam trains (around 150kph?) and industry based around steam engines. Iron and steel are widespread, and all countries in Esia have access to this technology. Messages are still delivered by magic pigeon, who can fly 200kph and don't tire.

The walls will be built for 1500 years, with the lots of reinforcement in the last 300 years due to increased tensions and steam power for the last 200. We'll also say the populace generally approves of these defensive measures, keeping morale decently high.

I was thinking of building a large stone wall similar to the Chinese Great Wall, but the consequences of having a limited supply of troops (only 40 per km) really hinders progress. On the other hand, fireballs could easily destroy siege towers, and with an effective steam railroad, reinforcements could be shipped in quickly.

I guess the final question is: Could a China-style wall with a railroad for transport and magic be effective repelling against armies 5 times the militias size? If no, what option would be effective?

A side note, technologies using steam not mentioned can be used by both sides if reasonable. I personally feel that defense will be easy with a steam railroad, but I'm not sure if I'm overestimating the capacity of trains.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – L.Dutch Sep 11 '18 at 14:52
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The only way I see this working, is if your forces were mostly composed of mages, far outnumbering the mage count of the enemy. This is because your mages are basically walking cannons, who can fire 60 fireballs a day, as fast as they want. This means that when the enemy attacks, you want to make sure you are sheltered from their infantry and have an advantage over their mages. A wall would provide you with the necessary defense and height to achieve this.

Your fireballs and lightning sound like a pretty effective defensive solution. The enemy would sustain massive damage, especially if a fireball can kill multiple people. and since every mage could fire 60 fireballs, you could theoretically fight off an army 60x larger than yours (assuming you have enough time to get into position and each mage fires off all their fireballs and each fireball hits and kills someone, yada yada).

Basically mages would just replace all your infantry (only 4 years training is really quick, and they don't need much equipment) and defensive battles would be very advantageous to mages as the defender can stand and throw fireballs while an attack must first move into range then throw fireballs while already being fired upon.

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  • $\begingroup$ The walls will be built for 1500 years, you did not considered this didnt you? $\endgroup$ – Mr.J Sep 12 '18 at 2:41
  • $\begingroup$ @Mr.J Anything that is built and meant to last needs to be maintained. Even the great wall of china needs to be maintained. Assuming its an active part of the defensive effort I don't see why they wouldn't be actively maintaining it and replacing worn and broken down parts. $\endgroup$ – Shadowzee Sep 12 '18 at 3:08
  • $\begingroup$ I thought it was meant as "I will be building this structure for 1500" $\endgroup$ – Mr.J Sep 12 '18 at 4:56
  • $\begingroup$ @Mr.J Well that would be impossible.... 1500 years and the last 300 years with active use without maintenance would wear down any structure including stone and metals. $\endgroup$ – Shadowzee Sep 12 '18 at 5:09
  • $\begingroup$ That's what I think, and a complete waste of resources if you ask me. Because he used will be built rather than have been built. O the confusion! $\endgroup$ – Mr.J Sep 12 '18 at 5:16
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Honest Answer:

No

Why are you going to build a wall for 1500 years? if Attackers will be 6 months or so, then your casualties will be high, and also the upkeep needed to keep those people alive. If you have vast resources, WHY NOT ATTACK THE ATTACKER WITH A FULL SCALE WAR? You have your technology, you have your mages. In over 20 years you have trained thousands or millions of fire or lightning mage at your ranks. With the resources of building a wall into funding or making armors for your troops, you'll be more powerful than them.

Lets say you built that wall, and you'll be defending every 6 months, thats... I think, a completely waste of time because as long as your empire is around, attacks will happen. That's why most of our history, walls are not built. Instead, we research about a more powerful weapon or armor that we could use to arm our armies so that they can end the war by obliterating the enemy.

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  • $\begingroup$ Fair, but I was hoping to have a more "no wars of invasion" policy. I was thinking of it in the Chinese way where attacking the nomads would take too long for too little gain. Is it unreasonable for such a defense that it couldn't be handwaved? $\endgroup$ – QuyNguyen2013 Sep 11 '18 at 4:14
  • $\begingroup$ @QuyNguyen2013 big walls have huge risks, from manpower to resources, you'll have to account those during war. As posted by another answer, you have the best offense in your arsenal, why not use it to gain everlasting peace? It would be more interesting or possible if your keeping natural elements from entering your country e.g wall for waters because these walls would increase survival for your citizens and noone would even dare to tear it down. But a wall to keep enemies at bay? Have you considered your enemies using siege machines? $\endgroup$ – Mr.J Sep 11 '18 at 5:09
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    $\begingroup$ @QuyNguyen2013 fun fact: the Chinese did attack, make treaties with, and otherwise attempt to pacify the nomads, and I can think of at least two occasions upon which they were conquered by the nomads. Lots of their best generals were deployed on the frontier, and the Great Wall, while effective, cost thousands of lives and centuries of time to build. The xiongnu became a real threat around Han dynasty and they were attacked, as well as Korea and Tibet. $\endgroup$ – JavaScriptCoder Sep 11 '18 at 13:35
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Yes.

The best way to break down a stone wall is to apply force. A battering ram is fine but the defenders above will make hash of you. Better to keep a safe distance and use a siege cannon.

siege cannon https://www.pinterest.com/pin/541346817688221463/

But your world does not have siege cannons. Fireballs are great vs animals or plants but stone does not burn and fire is just hot gas with minimal mass. Lightning will not do much to stone. Attackers might built Roman-style siege engines but these are cumbersome and less effective than cannons.

A border wall would work fine for this non-cannon world, just as it did for the Chinese and Romans. That said, a world with tech to make pressure-worthy steam boilers has tech to make a cannon. Maybe a steam powered cannon? That would be a cool thing to have develop midway thru the store.

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  • $\begingroup$ And that steam powered cannon will be created by the enemies for some 20 years or so, while he on the other hand is still building his wall. So after his wall was built, its completely surrounded by steam powered cannons ready to break it down. Hence, he should have built the cannon first, attacked the attackers so that his land will be safe. $\endgroup$ – Mr.J Sep 12 '18 at 2:38
  • $\begingroup$ @Mr.J - If the Chinese who built the Great Wall decided to track down and extirpate the people on the far side they feared, where would they go to attack? Nomad camps? Farms? It is very difficult to wipe out a decentralized threat. $\endgroup$ – Willk Sep 13 '18 at 12:50
  • $\begingroup$ 800 000 men, soldiers and civilians are used to build the great wall with 2000 or more years used to build it. If these resources was used to survey China's land that would have been possible, and why will they attack nomad camps and farms if it was not a threat? sure a nomad camp might be a enemy encampment, but if its small enough to be considered as a threat, why attack it? But if its large enough to be a small army, might as well ask for their alliance, then kill them if they dont agree with your terms. $\endgroup$ – Mr.J Sep 14 '18 at 0:26
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The purpose of a defense is not to defeat an enemy force. The purpose of a defense is to deter that enemy force, or to buy time for a friendly counterforce to be prepared.

In other words, the invading general, looking at an enormously expensive wall guarded by a paltry few defenders, will simply laugh. The wall is not a deterrent, it's merely an obstacle to be reduced (or blown) by the engineers...a few minutes' delay.

In the Era of Steam, the best weapons used machined components and ammunition, and concentrating firepower to win against enemy forces meant that too many soldiers were concentrated together to survive by pillaging. So armies needed supply lines of food and ammunition to be effective. And those supply lines are always vulnerable.

Continental supply lines (before trucks) used three methods: River steamboats, railways, and pack animals/wagons. Steamboats were preferred (cheapest, fastest, most flexible), so the defender's fortifications should focus on denying enemy use of rivers instead of bridging the entire gap. Defensive forces can also conduct spoiling attacks against railway construction camps, can ambush wagon trains, shoot down pigeons and runners, and destroy every enemy telegraph line they run across.

Once the enemy's military objectives are clear (town X, river junction Y, access to railroad Z), the defender can focus defensive efforts more clearly. But the defense must retain mobility for spoiling attacks and deception operations.

Remember, the purpose of the defense is to slow (not defeat) the invaders, buying time for the invasion-smashing counterforce to get organized and fitted and travel to the front.

Once the counterforce arrives, the defender's own steamboats and railways permit strategic movement, the ability to mass faster than the slowed enemy, and the defender can destroy outlying invader forces (limiting the invader's options) with minimum risk. Cut the invader's supply line entirely, blind them by eliminating their scouts, then lead them into a nasty trap.

One word about steam trains - they can transport a lot of troops quickly, and a lot of supplies...but they also require a lot of planning and preparation, and they are not very flexible. Rail is expensive to build (and repair), and fairly easy to degrade or destroy. You are limited by the rolling stock available, by what's already on the rails (and in what order it is travelling), and by the existing railside facilities for loading and fueling. If two railrods have different gauge (common before 1880), then the entire trainload must be transshipped...assuming somebody made sure the same kinds of cars would be on the new train! If you have a trainload of ammunition arriving, but aren't ready to transload it for the rest of it's journey to the front, then you must warehouse it (out of the weather) so you can free the track space for the next trainload of, say, food. Without a really good organization, rail networks can quickly be congested and snarled terribly...another reason why steamboats were preferred.

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YES! I'm assuming you have some basic characteristics similar with China to even posit a wall.

  • You have a large attackable perimeter
  • You're overpowering but not quite so much if you spread the army along the entire border (assuming no walls)
  • You have the resources and time

If every person stationed on the wall just had to build a house-sized portion then this would just be a resource issue. So amount of available rocks nearby would be your limiting factor.

BUT MORE IMPORTANTLY! Consider America's transcontinental railroad thats a railway over 4x longer than yours built in just 6 years with just 4000 people. You want to do this with 40 people per km over 700km or 28000 people. By all estimations you should finish in 4 months if all your resources are being made at a fast enough rate.

Granted that's just for a railroad. But you could take proportional figures for stone walls of a certain height, ditches of a certain depth, and railroad. If the railroad is helping you move rock for the rest of the wall then it's not even a factor about height so much for the stone since it already starts at the highest point. And ditches were never necessary to begin with.

For the walls to be built at a pace even slightly related to a railroad building pace you'd need to transport rock via train, then drop the slab off the sloped edge of the end of the track. Stacking on an incline (only thing I could find). Which means only the top layer needs special consideration. And since we know the cleaner the joint the longer it last/more solid it is, maybe have it polished on inner faces during transport. (Not finding a good reference for this, but I know I got the info from learning about the pyramids when I was younger, Khufu specifically I think) All in all I would say simplified: tipping a rock over an edge, straightening, and capping; would take at most 465 times longer.

I had started with an assumption based on length transport, if an empty cart can be de-railed and move around a full cart then the difference is mostly travel time. Then I realized you could add more carts to de-rail. So the difference is mostly weight transport it would seem. I believe I've seen 30 beams on a transport cart before. A single beam could have roughly a length of 12m and roughly a weight of 65kg/m. So a weight of 715kg/rail for a total of roughly 1500kg for a 12m length. 22 cu ft of granite meanwhile, is roughly the same weight. So if we want a wall section 12m long and approximating the Great Wall of China with a 16ft square cross-section... then we have 465 the weight of material to move for the same length of wall.

It comes down to having a large enough quarry really. Also can any of your magic help you with this process? Fire for expanding cracks in stone and other things to speed up portions of the process?

BUT IN REALITY: You'd want short-term solutions as well as long-term. So you'd be building guard posts or mage towers regularly spaced along your perimeter. And these would probably take longer to build. And you'd probably fill in the gaps between major outposts with minor ones, etc. The only way you'd jump right to wall is if there was no point in building an outpost (high-death/low-reward). Looking at towers as full-blown castles one could expect 3k workers to take 2-10 years so dividing them into chunks you could build 9 border towers every 6 years. If visibility is 15km on a good day. Then building every 15km over 700km would take 5 cycles or 45 years.

So if you did towers followed by a wall/railroad combo (or maybe the reverse for transportation of resource reasons, but then there's no short-term gain). You'd be looking at 45 years for towers, 155.5 years for wall, and .5 years for rail. Or 201 years to finish major fortifications. I'd assume there's some engineering tricks you could use to reduce the wall time and you could cut out the towers as well. One trick I might use is a hollow wall and dumping sand, rock, and clay from the bottom of a cart to fill the wall. It wouldn't surprise me at all if someone could get this done in their lifetime with a workforce of 28000 under their control. After all, even unskilled workers become skilled over a long time at a single task.

So is a giant wall a viable for repelling 5 times the invading force?

Yes, the speed at which you can build the wall with your tech level is very high, and while setbacks could happen, this means that getting the project going looks more like a short-term gain and so it's much more likely to happen. Such a wall would need to be manned, but 40 people per kilometer is actually quite a bit. People would be in visual range of each other. That means the odds of you losing a section of wall without knowing about it in progress is extremely low. The railroad is delicate, but having it as quick transport means your enemies need to fan out and attack multiple points to reduces its effectiveness as a transport method. The rails provide a decent rod for lightning attacks. Fire is generally not greatly effective against stone and steel. A lip on the wall could provide significant cover considering these things. Also, there's no physical projectiles because of magicians curtailing development, so all in all you're extremely technologically advanced in defense with just a simple wall. The secure ground, various cover options, and height it gives to your troops is considerable advantage. They also have a tactical retreat option if absolutely necessary, funneling through a captured portion of wall is going to be slower than retreating off the wall most of the time.

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  • $\begingroup$ I'd be skeptical of my number too. But that's what it ended up breaking down to be. The train is probably the single greatest factor compared to the time required to build The Great Wall. I'd assume that's why the Transcontinental was built so quick as well. $\endgroup$ – Black Sep 11 '18 at 19:18
  • $\begingroup$ again... The walls will be built for 1500 years, Thats just the wall, the train is not even considered. $\endgroup$ – Mr.J Sep 12 '18 at 2:43
  • $\begingroup$ @Mr.J Yeah, just saying that since you could theoretically do it all so fast with the OP's tech level it becomes all the more viable. Humans like short-term gains. $\endgroup$ – Black Sep 12 '18 at 20:19
  • $\begingroup$ Now that I think about it I should probably put that in the answer. :d $\endgroup$ – Black Sep 12 '18 at 21:42

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