[Martin Kallander]

It makes no sense to me, surely the weight of a stone castle would be way to much for an artificial earth mound to support? Why don't these castles displace the earth and sink into the mound over the centuries?

[Anthony Clipsom]

[Martin Kallander]

So the solution was basically just to build something small that wasn't too heavy? Were there any other methods to allow greater structures to be created on the mound, like for example, the mound being surrounded by a thinn wall so as to not give the earth anywhere to go?

[Dan Howard]

After a few decades, the mound is no longer "artificial". It has been weathered and compacted enough to be indistinguishable from natural hills. Castles on these hills do not sink for the same reason that castles built on natural hills do not sink.

[Martin Kallander]

Well that is news to me, I thought castles on normal hills did sink if the hill didn't have a stone core. Aren't you ideally supposed to dig until you reach bedrock before building something like a castle?

[Dan Howard]

[Jean Thibodeau]

Just speculation on my part that if the mound wasn't too high, had already been used for decades or more with only a wooden Keep and stockade wall near the top, when later the castle was upgraded to being made of stone, one might dig a foundation reaching the original ground level or even deeper ?

One reason might be to include a well at the bottom to reach ground water ? ( Probably a good idea in any case to dig a well first before creating the hill mound around it: Easier to do that than digging the well after creating the mound ? )

Alternatively in my imagination the original making of the mound could have been done around a hollow wood lined core with the intention of the core being at a later time being relined in stone and form the foundations of the Keep to be built a generation or two later ? The initial hole to reach ground water with a well ?

The walls surrounding the Keep at the top of the mound would not really need a foundation reaching the original ground pre-mound level ?

On the other hand the simplest answer is that the mound between the time of the initial wooden fortification and the replacing with stone would have settled and become as solid as a natural hill ? ( As mentioned in earlier posts. )

Oh, building the mound could be done like for some Celtic forts where wooden frames would be filled with soil, maybe clay and rock, built up in concentric smaller and smaller diameter layers, the outside of the mound covered with clay or earth where grass would grow hiding the inner framework.

By the time the inner wooden interlocking beams rotted the whole mound of earth, clay, small and large field stones would have become firm and solid ?

OK, a long purely " Theoretical Post " not supported by evidence just for the fun of it. Just how I would do it if I was a Motte & Bailey engineer in period.

[Anthony Clipsom]

Here is an example of a cross section of a keep on a motte to help visualisation. It is Clifford's Tower in York



Note in this case the layers of the motte, where the foundations go, the well and the work the Victorians had to do to stop it falling down (The concrete reinforcement A and the enclosing walls are Victorian repairs).

[Matthew Amt]

There's no real nead to speculate, since there are literally hundreds of examples in the UK alone. I was even on an archeological dig at one back in 1983, Hen Domen at Montgomery, Wales. It's a cute little place, though now like many others, nothing remains of the wood and clay buildings, just the earthworks.

It's been too long since I read up on things like this, but I expect they never tried to build with stone on a fresh motte. Many many castles were built with timber and clay walls and buildings, though many were certainly rebuilt in stone in later generations. As others have said, that's the main issue--you have to wait until the motte is settled and solid to put anything stone on it.

There were also a few keeps that were built on flat ground, and the motte piled up around the outside. So you'd get the same visual (and defensive) effect. In at least one castle that I've been to, that mound was later removed and a door installed at the new/lower/original ground level. The changes are visible in the stonework.

You can certainly build a stone castle that is not on bedrock, it's just a matter of making proper solid foundations. But of course castles *tended* to be built on high spots, which are usually going to be rock outcrops.

But I *don't* think you want to try building up generations of "rotting timbers" and expecting that to be structurally sound. Medieval engineers had plenty of practice and some spectacular "fails" to learn from, and pretty much knew what they were doing.

Matthew

[Martin Kallander]

[Matthew Amt]

[Martin Kallander]

[Matthew Amt]

[Martin Kallander]

[Anthony Clipsom]

[Matthew Amt]

[Martin Kallander]

[Jean Thibodeau]

Oh, the way a motte might be created can depend a lot on what the builders start with.

A) Flat ground build up from dirts, stone, clay, and a mix of whatever materials where available.

B) The suggested solution of building a very high stone tower and creating the slopped motte around it so that the foundations are on the original hard ground and/or down into solid rock.

[Toni Šušnjar]