# Moat Dimensions (and the fauna therein) **URL:** \ **Category:** Factual Questions\ **Created:** [October 9, 2026, 6:33pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706 "2026-10-09T18:33:47Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [October 9, 2026, 6:33pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/1 "2026-10-09T18:33:47Z")
We’re all familiar with the trope of the moat surrounding a castle (or keep); the water-and-occasionally-crocodile-filled trench that surrounded medieval strongholds. How common were they? How wide were they, as a general rule? How deep did they tend to be? What dangerous aquatic fauna were they usually stocked with, in order to discourage skinny-dipping? ---
**Author:** ![Filbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/filbert/32/3433_2.png) [@Filbert](https://boards.straightdope.com/u/Filbert)\ **Post date:** [October 9, 2026, 7:30pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/2 "2026-10-09T19:30:15Z")
Castles and keeps with moats were pretty common in Europe, although the crocodile/hippos/piranha filled bit is sadly a myth. It’s hard to know _how_ common moats were as a lot have been destroyed, or at least the surrounding lands have been sold on and old defensive ditches filled in as they became less useful. We have records of them existing, remnant bits and still the odd place like [Caerlaverock](https://en.wikipedia.org/wiki/Caerlaverock_Castle) where the moat is still there. There’s loads of geese in the area due to the nature reserve, which can be a bit aggro-ey, if that counts as dangerous? As for how wide and deep, well, it depends. The basic cliche concept is based on a very common design style known as ‘[motte and bailey](https://en.wikipedia.org/wiki/Motte-and-bailey_castle)’; the idea of a castle raised up on an artificial hill, surrounded by a ditch. The idea was to make it hard for anyone to get up to the walls in force, especially with anything that could enable an invader to climb walls or bash through the door. Often the ditch surrounding them wasn’t even full of water, it was just a trench dug out to make the topography a bit more awkward for invaders. There were loads of variations on the concept though, including using or diverting a bit of existing river to go partly round the castle. For the really antisocial, sticking the whole castle on an [island](https://en.wikipedia.org/wiki/Eilean_Donan) in a lake also worked as basically a free moat. You can hardly walk round in the UK without tripping over a medieval castle. ---
**Author:** ![Banksiaman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/banksiaman/32/3334_2.png) [@Banksiaman](https://boards.straightdope.com/u/Banksiaman)\ **Post date:** [October 9, 2026, 7:37pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/3 "2026-10-09T19:37:27Z")
Just having done a bit of a castle crawl, wet moats were far less common than dry moats. They could be moving, by either using an existing island in a river or tidal sea or cutting a new channel that moved water, or it could be still. I think the health of the inhabitants living next to a big stagnant surrounding lake in which they discharged all their sewage, animal waste and crud would be pretty dire. Dry ditches were usually V-section cuts up to 5-10 metres deep with the fill forming an additional mound behind, so leaving you with a 10-20 metre climb. The profile was usually as steep as the local parent geology could remain without slumping, so sometimes very, very steep. The deeper and shallower the ditch the wider it would have to be, so at least 1:1 depth:width, but potentially 1:2. I expect a few limited species of fish could be farmed within the moats, if you like your catfish turdy. Your average crocodile would be very sluggish in the cold and would soon be made into someone’s decorative leather jerkin. ---
**Author:** ![zimaane](https://avatars.discourse-cdn.com/v4/letter/z/a3d4f5/32.png) [@zimaane](https://boards.straightdope.com/u/zimaane)\ **Post date:** [October 9, 2026, 8:46pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/4 "2026-10-09T20:46:18Z")
The concept of a defensive ditch predates the concept of a castle by centuries. Villages in Iron Age Europe typically were enclosed by an earthen wall surrounded by a ditch, all to deter attacks from neighboring villages. The ditch was dry, although I’d guess in times of heavy rain it might fill with some water. Castles usually had moats and sometimes they were deliberately filled with water. As noted above, they wouldn’t have crocodiles or piranhas, but would have been full of garbage and sewage. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [October 9, 2026, 9:06pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/5 "2026-10-09T21:06:39Z")
I’m in Japan right now and for someone who really only knows moats from their depiction in film, TV, and comic books; the moat around the Imperial Palace seems absurdly wide - about 60-70 ft, I would guess. Is that just because of the importance of the Palace, a Japanese thing, or were even some European moats that wide? As for the fauna found in a moat, I visited a small castle town in the Czech Republic that had a dry moat occupied by bears. > **[Castle bears in the Czech Republic – Bears in Mind](https://www.bearsinmind.org/en/projecten/ending-a-centuries-old-tradition-in-cz/)** ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [October 9, 2026, 9:20pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/6 "2026-10-09T21:20:56Z")
> [@Filbert](#): > > Castles and keeps with moats were pretty common in Europe, although the crocodile/hippos/piranha filled bit is sadly a myth. Exactly. Those sorts of animals weren’t native to Europe, and even if some enterprising noble tried to ship some in, they wouldn’t have lasted for long. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [October 10, 2026, 5:08pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/7 "2026-10-10T17:08:23Z")
Edward the Twelfth wasn’t known as the Piranha King for nothing… ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [October 10, 2026, 7:24pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/8 "2026-10-10T19:24:20Z")
> [@Filbert](#): > > There’s loads of geese in the area due to the nature reserve, which can be a bit aggro-ey, if that counts as dangerous? Geese are often used as guard or watch animals because they are quite territorial and will loudly honk at intruders. Supposedly geese saved Rome from a Gallic invasion in the 390s BC by honking and awakening the Roman army. ---
**Author:** ![Ancient\_Nerd](https://avatars.discourse-cdn.com/v4/letter/a/ed655f/32.png) [@Ancient\_Nerd](https://boards.straightdope.com/u/Ancient_Nerd)\ **Post date:** [October 10, 2026, 9:36pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/9 "2026-10-10T21:36:35Z")
> [@mixdenny](#): > > Edward the Twelfth > **[Edward VII](https://en.wikipedia.org/wiki/Edward_VII)** > > Edward VII (Albert Edward; 9 November 1841 – 6 May 1910) was King of the United Kingdom and the British Dominions, and Emperor of India, from 22 January 1901 until his death in 1910. The second child and eldest son of Queen Victoria and Prince Albert of Saxe-Coburg and Gotha, Edward, nicknamed "Bertie", was Prince of Wales and heir apparent to the British throne for almost 60 years. During his mother's long reign, he was largely excluded from political influence and came to personify the leis... Have there really been five King Edwards since 1910? ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [October 10, 2026, 9:52pm UTC](https://boards.straightdope.com/t/moat-dimensions-and-the-fauna-therein/1033706/10 "2026-10-10T21:52:04Z")
> [@Ancient\_Nerd](#): > > Have there really been five King Edwards since 1910? Just one, briefly; but if you count the three Saxon Edwards (the Elder, the Martyr and the Confessor), you have a total of 11, which is _almost_ there.