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Imagine some settlers are looking to build a castle in an area of expansive plans discover a small, isolated mesa: the formation has a very steep face, rising up 10-20m. The area of this formation just so happens to have just enough surface area for the castle they would build there. The builders would construct an sort of earthen ramp along the face of this formation to be able to reach the gate. However, there is also the rest of the vast plain where they can build the same castle at the same elevation as everything else.

Generally, holding the high ground in battle is advantageous, as Obi-Wan et al. have proven. In this case, are there inherent risks to building an elevated castle that one on flat terrain doesn't need to consider? Is the extra visibility a concern? Given medieval weaponry as advanced as catapults, crossbows, etc., is there a serious threat of undermining the walls? What if early gunpowder weapons like cannons are introduced?

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    $\begingroup$ There would of course be even less escape if besieged and getting the stones/wood up there requires more energy. But why would a group of settlers build a castle? $\endgroup$ – Raditz_35 Aug 17 '17 at 13:24
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    $\begingroup$ I'd call that poor word choice on my part, at worst. The scenario was more meant to describe the geography in question than the people, so I didn't really consider that detail important. $\endgroup$ – MSet Aug 17 '17 at 13:35
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    $\begingroup$ Castles were always built on hilltops or other natural elevated terrain if available, provided there was a source of water, or else there was enough rain and sufficient area to built a rainwater cistern (plus catchment area of course). If a natural elevation was not available they built an artificial one. Buried fortifications are 19th century or later. Ancient and early medieval artillery was not a serious threat to well built walls. Undermining the walls was always an option if possible (that is, if the castle did not sit on hard rock), the besieging army was serious and had enough time. $\endgroup$ – AlexP Aug 17 '17 at 14:12
  • $\begingroup$ In the interest of giving you something you can use for your story, maybe susceptibility to lightning strikes would be a weakness? Perhaps if that interacted with the particular forms of magic or technology attackers would use? $\endgroup$ – workerjoe Aug 17 '17 at 18:19
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    $\begingroup$ Why even create a castle on top? You could rather excavate and create a tunnel for access. $\endgroup$ – Anoplexian - Reinstate Monica Aug 18 '17 at 15:04

14 Answers 14

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Consider Masada

enter image description here

This fortress was broken only by the Romans building an extra ramp up to the top of the mount and moving siege weaponry up said ramp. A fortress built in such a location can be as impenetrable as fortresses come.

The problem being that, as General Tacticus said,

If the enemy has an impregnable stronghold, see that he remains there.

The fortress may not be broken but you're not doing a lot while you're holed up in it. So only the usual food, water etc. as the standard weaknesses of a fortress under siege.

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    $\begingroup$ This is the exact answer I was going to give. The 'snake path' leading up to Masada makes assault nearly impossible. Masada also had large cisterns and storerooms so it could be stocked with months of water and food. $\endgroup$ – Andrew Neely Aug 17 '17 at 14:51
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    $\begingroup$ The "Cloud People" of the Andes had a similar "castle" at the top of a mountain ridge. Rather than a ramp or path built up the fact of the cliffs surrounding it, they had narrow, steeply sloped slots that everyone entering had to climb. $\endgroup$ – Michael Richardson Aug 17 '17 at 16:32
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    $\begingroup$ Note that the ramp that the Romans built only worked because they were building the ramp with Jewish slaves: people who were ostensibly family and kin with the defenders. The defenders of Masada were also few in number (less than 1000 including women and children, compared to the 4000 Roman soldiers) but were relatively well supplied (they had water to bathe and wash with, the Romans did not). I've also been to Masada. Very interesting place. $\endgroup$ – Draco18s Aug 17 '17 at 18:28
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    $\begingroup$ That last sentence in this answer is the key weakness of such a fortress: most of the time, you're not under siege, and the fortress serves as a base of operation for patrolling cavalry and soldiers, and probably as an administrative center as well. If it's hard to get in and out of the fortress under normal conditions, that hampers its usefulness. $\endgroup$ – bgvaughan Aug 17 '17 at 22:29
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    $\begingroup$ @bgvaughan the point usually is that it is easy to enter/exit when you control the castle. If path leading to it is narrow and in the range of fortifications you may have hard time approaching it with siege weapons when defenders are free to drop arrows/stones/hot oil/dead cattle on you but might be perfectly traversable when you are not under fire and use easily removable bridges and stairs. $\endgroup$ – Maciej Piechotka Aug 18 '17 at 14:22
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TL;DR: Erosion of the mesa itself.

As luck would have it, this time last week I was visiting a castle that's almost exactly as you describe. It's called Bamburgh Castle, is located in the north of England, and has existed on the same site in some form or another for around 1400 years. It was built atop a large outcrop of stone (chitstone, I believe), with a stone path leading up to the main structure.

enter image description here

However, chitstone is not particularly weather-resistant, and Bamburgh Castle is located right next to the North Sea:

enter image description here

Due to a combination of human activity and natural erosion, the rock the castle sits on has gradually weathered away to the point that one wall was actually undermined and partially collapsed. It's been rebuilt, and the trust that oversees the castle have sprayed the exposed rock with concrete in an effort to stop the weathering.

So my answer is erosion. It's a long-term weakness, certainly, but it's a weakness that castles built on flat ground generally don't have to worry about, so I believe it fits your criteria.

(As a final aside, Bamburgh Castle was the first British castle to fall to cannon fire, during a nine-month siege as part of the Wars of the Roses in 1464. So to corroborate Separatrix' accepted answer, your castle would also be vulnerable to siege warfare.)

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  • $\begingroup$ Usually, erosion in the next 500 years is of little concern compared with war in the next decades. $\endgroup$ – Pere Aug 17 '17 at 21:05
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    $\begingroup$ While it may take hundreds or even thousands of years for wind and water to wreak a wall, it may only take a few days for some well-placed digging to do the same. If a sapper team can get under your mesa, they can bring down anything they'd like, as long as the rock is soft enough. $\endgroup$ – ArmanX Aug 17 '17 at 22:05
  • $\begingroup$ As mesas are often formed of a thin slice of hard material over something soft and easily eroded, the castle is at great risk from mining (in the original sense) or especially if a nearby river is diverted (as Genghis Khan was wont to do) to wash its support away. $\endgroup$ – Brian Drummond Aug 20 '17 at 18:44
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This was done in France with a castle called Mont Saint-Michel, and it's surprisingly effective.
Disclaimer: Most mesas have a river, but not a tide cycle. It's not unheard of, though. enter image description here

As you can see, this castle was created on a small patch of raised land, which happens to be located in the Normandy territory of France.

This castle was built with the tide in mind. Every 12 hours, the tide would rush in and everyone not in the walls would become stuck and wet. This means that laying siege to this city is insanely hard, as all land within a ~5km distance is flooded.

The inherent danger to this, is occasionally, the city itself would find its own feet wet, and of course, not being able to go outside means many diseases.

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    $\begingroup$ Cool. Probably every 12 hours though, right? $\endgroup$ – Chris Chudzicki Aug 18 '17 at 4:04
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    $\begingroup$ Note that nowadays there is a road to access Mont Saint Michel which is only submerged during exception high tides, so that it is on an island only a few times a year (Equinox, you have to reserve a year in advance ;)). I suppose that much like Masada, a determined army could build such a ramp. Also, bonus points wrt Mont Saint Michel: it's surrounding by sands (hell to move any artillery through), with the occasional quicksands (tourists beware). $\endgroup$ – Matthieu M. Aug 18 '17 at 9:25
  • $\begingroup$ The area around the "island" is a dangerous place. The tide definitely rushes in here. There are some cool time lapse videos on You Tube. There are warnings not to go out on to the sand, because of the tides and quicksand. $\endgroup$ – Mohair Aug 18 '17 at 18:40
  • $\begingroup$ @Mohair Didn't see those warnings last time I was there. Despite the 11 meter or so water height difference, it's quite safe to take a walk there. As long as you're back in time, that is. $\endgroup$ – Mast Aug 20 '17 at 20:52
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Generally, I can't think of anything wrong with it. The Japanese in fact built their castles in a similar-ish way (admittedly by shaping the hill itself and giving it the steep stone walled sides you see below)

Note that the grass area within the walls are at the same level as the fortifications.

The only risk I can imagine is if the rock/dirt making up the mesa just happens to be fragile in a particular location, or if there is a cave system underneath.

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  • $\begingroup$ A Dutch language print of Osaka... where did you find this? $\endgroup$ – Floris Aug 19 '17 at 19:35
  • $\begingroup$ @Floris: Obvious fake, as the text isn't contemporary with the image. And in fact Google can find larger images with the 3 textboxes not cropped, and the text "Casteel Ofacca" above the castle. But Casteel is old Dutch spelling, so that part seems correct. Source: Atlas of Mutual Heritage. And while we're at it, "Rechte beschryvinge van het machtigh koninghrijck van Iappan" (Rightful description of the mighty kingdom of Japan) documents the owner of Casteel Ofacca as "Inafacka 't Sonnokamy". Casteel Ofacca seems legit. $\endgroup$ – MSalters Aug 20 '17 at 14:45
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    $\begingroup$ I suspect that the "f" in "Ofacca" is actually the "old s" ("long, medial or descending s " - doesn't have the cross bar of the "f"). And as far as I can decipher the text boxes they are in fact in (old) Dutch too. So this is probably a "old postcard from an older print". $\endgroup$ – Floris Aug 20 '17 at 15:14
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    $\begingroup$ The Dutch were a major early trading partner with Japan. As a result there are a surprising number of Dutch loanwords in Japanese. Given the history it's not so surprising to find a map like this. $\endgroup$ – briantist Aug 21 '17 at 6:09
  • $\begingroup$ @Floris: I literally just googled for japanese castle images and this one demonstrated my point best. $\endgroup$ – Kyyshak Aug 21 '17 at 11:29
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Unless the mesa contains a natural spring to provide an unlimited water supply, your settlers might be wise to build out on the plain where there is water, rather than in the heights where there is not.

The mesa might also have disease-infested indigenous life such as rats or bats. Such infestations would be very difficult to eradicate with with medieval technology.

If your settlers do choose to build out on the plain, they will want to put some distance between themselves and the mesa, to keep any enemy from using its heights against them.

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    $\begingroup$ None of those are risks of elevation versus plain, just risks that are location dependent. $\endgroup$ – The Nate Aug 17 '17 at 15:25
  • $\begingroup$ Good point, so these people should build Motte-and-bailey castle, which consists of a stronghold on a hill, and adjacent lightly protected courtyard. Water will be available in the courtyard, and, in case the courtyard is lost, stored in the main keep. $\endgroup$ – Alexander Aug 17 '17 at 16:41
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    $\begingroup$ Yup for water. Quote from wiki Hillside castle: "The advantage of a hillside castle was that its well was much less deep than that of a hilltop castle. The boring of the well was often the most expensive and time-consuming element in the overall construction of a castle." $\endgroup$ – Vashu Aug 17 '17 at 23:36
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    $\begingroup$ +1 for mentioning water mesa are not like hills they rarely have access to ground water, most have to rely on capturing and storing rainwater. $\endgroup$ – John Aug 19 '17 at 14:16
  • $\begingroup$ Medieval rat control - cats. Not sure it's that hard. Mice live everywhere. if you don't have control and with enough food they will be a problem anywhere. I haven't heard any place where people live without mice and rats. $\endgroup$ – akostadinov Aug 21 '17 at 13:04
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The real problem is that generally people only want to do so much work or walk so far in a given day. You can call this a "human factors" issue. Anyone who is living a pre-modern lifestyle has to deal with moving water, clothes, crops and tools significant distances if they don't live directly where they farm or work. And in a society like this, generally 90% of them are farmers. Specialized fortresses like you are talking about can be be made to work, but often must take special efforts to supply and keep secure. The people doing the daily stuff--including guarding the place--are likely to be annoyed by the distances they must move and carry stuff. As a consequence, they are likely to damage the inherent security of the place by creating all kinds of shortcuts through or over what should be secure walls.

Alternately, when the place is truly inaccessible and secure, it usually gets abandoned after a while, as people doing the real work move away and the rulers cut cost by forgetting about those inconvenient places. You can tell this by the fact that there are many, many forgotten fortifications around the world. Archaeologists are turning them up all the time.

So to sum up: you can make great fortresses, but a good and practical fortress is close to where the people are. Those are the ones that will be in use centuries later.

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The disadvantages are mostly economic.

  • Getting goods up/down there is expensive and takes time.
  • More expensive to build.
  • Maintenance is more expensive.
  • Establishing the castle as a trading hub is very difficult.
  • Having access to groundwater is less likely, limiting the number of troops that can be supported.

There are some direct military disadvantages as well:

  • Launching counterattack on the besieging army becomes very difficult.
  • Sieging the castle by starving them out becomes much easier (just need to block the single exit).
  • Much harder for the castle to let reinforcements join them during a siege.

All in all, these locations are great for monasteries, which are less affected by the downsides but still need protection from raiders.

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  • $\begingroup$ +1 for menioning multiple inherent risks as asked in the OP. $\endgroup$ – 8DX Aug 21 '17 at 13:58
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A Volcanic plug also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising volatile-charged magma is trapped beneath it, and this can sometimes lead to an explosive eruption. Glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the opposite side. Such landforms are called crag and tail. If a plug is preserved, erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform.

These were preferred sites for castles. Someone called them the nuclear weapons of the Middle Ages. There is little risk of undermining the walls.

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When your castle wall is at the edge of a cliff, it would seem more difficult for an enemy to approach than if it were on a (less steep) hill. But it would be easier for them to avoid detection and/or to dig under.

But notice that San Marino lasted nearly two thousand years on such a cliff.

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Aside from water supply issues, undermining is the main concern. The castle's vulnerability to undermining depends on the composition of the mesa, plus whether any factors in the landscape make erosion/undermining attacks easier. If it's possible to divert a nearby river & the mesa is not made of strong rock but something more crumbly, then it should be possible to destroy the defensive walls in only a few days by that technique. A hard rock foundation is going to be a lot more secure.

Since I don't know exactly how advanced the attackers are supposed to be, here's a good rule of thumb to decide if they could destroy a castle built on a strong rocky mesa: Ask, could they tunnel thru a mountain, like in the early railroads? If so, they can probably destroy a castle built on a mesa. Otherwise, the castle probably has the advantage

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Lightning - there are still arguments about the best way to protect against it, but back when castles were build, nobody had a clue. Maybe have a tower with metal you need to melt down? Or a religious symbol at the top- to give more meaning to the lightning.

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  • $\begingroup$ Especially since it's so high up. $\endgroup$ – Restioson Aug 20 '17 at 14:02
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One more historical example: Sigirya - the "Lion's Rock".

The stories about its exact origin and purpose are a bit unclear - it was supposedly built by Kashyapa, the king's son by a consort, who killed his father the king and usurped the throne from the legitimate heir, who fled. Fearing the heir's return, he built the fortress - a place of luxury at the top of a 200m tall rock with excellent views of the plains all around; strategically unassailable (picture from Wikipedia link above)

enter image description here

In the end, the brother returned with an army. Meeting him for battle in the plains, Kashyapa's army is said to have fled when they misinterpreted his manœuvre on his war elephant (to take a strategic advantage) as a retreat; seeing all was lost he committed suicide.

Moral of the story: don't kill your dad. And if you build a castle to defend yourself, it doesn't help you when you go outside.

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Without gunpowder this sort of Castle is almost impregnable. However, with the advent of cannons having a tall castle loses many of its benefits and gains many weaknesses see.

Gunpowder artillery in the Middle Ages

But this is not relevant for the early cannons, as they were far weaker than most seat reference at the time.

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A castle served several purposes. It is an obvious sign of power, it is a refugee in times of danger, and it is a command and control point for terrain. So it's location is critical. A mesa surrounded by steep walls on all sides is excellent for many reasons, but has some disadvantages.

For starters, on a large plain is the mesa located near a water source? Not only for water for daily use and in case of a siege (cisterns can be filled for this), but rivers are usually the main means of transport in the medieval era, so a castle ought to be situated to control river traffic. A mesa several days away from the main river in the plains isn't going to be in a good location to control it. It will also serve as a refuge for local farmers, so it needs to be located near the settlements.

Second, a mesa is great for defense, but if it is too contained then it can be itself surrounded and enclosed. The Romans did this at Alesia (as featured in a recent Hardcore History podcast). So while a mesa may seem ideal for defense, a site what has a flank protected by water may actually be better, since it allows for naval resupply, escape, and prevents physical encirclement.

Third, 10-20 meter cliffs may seem high, but this is only a delaying feature. Siegecraft was highly advanced in it's day, no defense was absolute.

But in general a mesa like this on an otherwise featureless plain was a good choice, one made many times. If a natural hill couldn't be used, folks would build one. There is a natural progression of these sites from a wooden motte and bailey castle to more permanent stone structures and walls. Of course out on a plain there may be a dearth of building supplies, so a mesa could be the ONLY defensive structure available, making it even more valuable until a stone quarry or brick making facilities could be built.

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