posted 06-01-99 03:35 AM
I'm not aware that any special engineering was used with building moats. They are simply deep ditches, dug with the usual picks and spades and the allowed to fill with water from a nearby water source. I areas of porous rock (limestone and chalk), or with no nearby water, castles had dry ditches. I can't think of an example of a medieval castle with has a puddled clay lining to keep the water in the ditch and since a besieger could easily break such a lining and drain the ditch it would have been of little use. Wet moats were at risk of being drained by besiegers and the dams that contained and controlled the moats had to be well defended, notably at Caerphilly and Kenilworth Castles. White Castle (Castell Gwyn), in Wales, http://www.castlewales.com/white.html has a wet moat with stone revetted sides, presumably to reduce the risk of the water eroding the footings of the castle (although, according to the CADW guidebook, the outer face of the gate passage fell into the moat at some point.).
Briefly the answer to you first question would appear to be that ditches were dug with temporary dams to keep the water out whilst digging and permanent dams to keep the water in afterward. They would presumably also have been dug in the summer when the water table was at it's lowest.Beaumaris is just above the water table and the level of the moat but I imagine that it can flood with some ease in the winter. But since the living accommodation is all on the second and higher storeys this is less a problem than it may appear. Beaumaris, whilst built within a marsh, is built on solid subsoil and is not particularly susceptible to subsidence although subsidence was a problem for many castles. Thus the answer to your question is that they built castles above the water and on firm land and that they didn't always get it right and that some castles did indeed have the walls washed out from under them.
Having said this wet moats are generally still water and don't have that much erosive effect so it is quite possible to build a motte and bailey and surround it with a wet moat and not suffer excessive erosion of the motte (all mottes gradually erode over the centuries through the action of frost, rabbits etc.). Some motte castles had wet moats although these are often now partially or completely filled in or the dams have broken and the moats are drained (Brinklow in Warwickshire is a possible example.)
However motte castles were built at a time when modern concepts of safety and planning consent were about as real as space flight. If you were planning to build a motte today you may find some difficulties with obtaining consent.
To get an idea of the tools that where used there is no better source than the Bayeux Tapestry with its illustration of men building a motte. See http://orb.rhodes.edu/schriber/b24.gif , where you can see men using pointed digging spades, rounded shovelling spades and an antler pick and http://orb.rhodes.edu/schriber/b23.gif (far right of picture) were you can clearly see that the digging spades were tipped with iron.
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Castle Quest
posted 05-31-99 10:11 PM
