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Author Topic:   The Keying of Wall Base
Erik Schmidt
Senior Member
posted 10-01-2000 09:55 PM     Click Here to See the Profile for Erik Schmidt   Click Here to Email Erik Schmidt     Edit/Delete Message
Does anyone have any information about how the bases of stone walls were keyed into sloping bedrock, such as an exposed rock surface on which many hillcastles rest?
I have seen only one example of a key "trench" cut into a stone surface, but it was only 25-30cm wide, which seems insufficient for a stone wall 1 or more meters wide. I would expect the key to be the width of the wall and cut level to prevent any outward force where wall and bedrock meet. Does anyone have a reference or have you seen one yourself? Thanks.

Senior Member
posted 10-03-2000 08:24 AM     Click Here to See the Profile for Merlin   Click Here to Email Merlin     Edit/Delete Message
Prof. Werner Meyer, specialist for swiss castles, held a speech on that topic at the university of Zurich some years ago. He showed us a whole collection of pictures, where one could see what you call key "trenches" cut into rock, sometimes with stairlike structures at steep parts. Mostly they hadn't the width of the castle wall, but just the width of the outermost row of stones, about 20 to 40 cm. Behind that, the bedrock was perhaps a bit flattend.

I visited a lot of castles in the northern Alsace-region (France), built on high rocks of red sandstone. There half of the castle was cut out of the rock itself (even big halls). The walls, built of the same material, fitted so perfectly on all edges that you sometimes couldn't tell the difference between bedrock and castle.

Even more extreme are the following examples of so-called 'cave-castles' in the swiss alps:




I too can't explain how the static of such buildings prevents them from falling. At its sides, the walls are just built along the rock. Maybe some else has an explanation?


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posted 10-03-2000 09:12 AM     Click Here to See the Profile for duncan   Click Here to Email duncan     Edit/Delete Message
The shear force is reduced by the key cut in the bed rock. The cut need not be too deep due to the thrust pressure applied to the top of the stone. This is the simplified and very uncomplicated version of stress dynamics which is a branch of physics.

Megan and Ralph

And in all your comings
and goings, May you ever
have a kindly greeting
from them you meet along
the road.
an Old Gailic Prayer

Erik Schmidt
Senior Member
posted 10-04-2000 06:06 PM     Click Here to See the Profile for Erik Schmidt   Click Here to Email Erik Schmidt     Edit/Delete Message
Thanks guys,
I wish I'd been to that lecture, Merlin.
I understand that the cut does not need to be deep, just horizontal to produce a direct downward force. What puzzles me is, as Merlin also states, the apparently narrow "trenches" used for such thick walls.
As we know, brick or stone walls have little resistance to sideways pressure.
If only the outer row of stones is bedded correctly onto sloping bedrock, one would expect the outward force(shear force) produced by the bulk of the wall resting on a sloping surface to force the base of the wall out, as a single(30cm) section could not hold it back.
The stair-like cuts on steep sections that you mention Merlin, would seem to be the way to bed the wall. Were they the width of the wall?
I visited a cave castle in Switzerland a few years ago. It looks like it may have been Kropfenstein, I was never able find out it's name.

Erik Schmidt
Senior Member
posted 01-07-2002 05:06 PM     Click Here to See the Profile for Erik Schmidt   Click Here to Email Erik Schmidt     Edit/Delete Message
I decided to revive the topic as I still haven't been able to track down any more info.

Merlin, do you think you could find out the e-mail address of Prof. Werner Meyer you mentioned above. I searched the web but was unable to find more than citations of his publications.


posted 01-08-2002 04:41 PM     Click Here to See the Profile for Peter   Click Here to Email Peter     Edit/Delete Message
Not mentioned is the greater width of all walls like this at the base, tapering towards the top. Thus taking away a lot of that stress.
This is still seen today in the building of drystone walls in the U.K. today, and no doubt other countries.

Senior Member
posted 01-08-2002 07:11 PM     Click Here to See the Profile for Merlin   Click Here to Email Merlin     Edit/Delete Message
Well, Erik, here it comes...
Meyer is a professor for medieval history and archeology at the university of Basel and the «icon» of all swiss castle-experts. Don't know if he's answering e-mails, though. But maybe worth a try:


Erik Schmidt
Senior Member
posted 01-08-2002 11:43 PM     Click Here to See the Profile for Erik Schmidt   Click Here to Email Erik Schmidt     Edit/Delete Message
Thank you for the address Merlin. I figured it would be worth a try to see if he can provide me with some info.

Peter, it may surprise you as much as it did me, that many castle walls are in fact not tapered.
I destinctly remember many castles in Italy, Switzerland and Spain which seemed to have untapered walls. If there was a taper, it was slight, possibly to allow for the wallwalk.

I have found the surviving fortified walls of most towns seem to also be untapered, for example;
Aigues Mortes
The roman walls of Lugo, in Spain, are an exception.


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