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A pretty straightforward question. I'm trying to find the largest drawbridge in medieval Europe, and it's more difficult than it seemed at first. At least I want to know if it would be possible to build a 10m long drawbridge with 15th century technology.

  • You may get more joy from HSM Stack Exchange or Engineering Stack Exchange. – Spencer Dec 14 '17 at 0:07
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    You might tell us what your research has shown so far, so we don't duplicate your efforts. Are you looking for something at or before 15th century specifically? Are you looking specifically for drawbridges on castle gates, or would drawbridges on bridges be included? – justCal Dec 14 '17 at 0:44
  • I"m focusing mainly in the late medieval period, but if it turns out that the largest medieval drawbridge was earlier i would like to find about it. So no, i'm not searching specifically for a type nor a period. My goal is to further understand the tecnological capabillities of that period, and to extrapolate what could possibly be made with those. Most examples I encountered show drawbridges as large as the gate they protect (4-5m aprox. at best) – Alex Krai Dec 14 '17 at 3:12
  • One of the sites I found with any currently active drawbridges is Helmingham Hall Bridges. These are also small-2.75 m span... – justCal Dec 14 '17 at 4:56
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    @AlexKrai I think it would be helpful if you mention the biggest one you've found already, so people know if they've at least found something bigger. – Semaphore Dec 14 '17 at 22:08
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The purpose of the drawbridge was to deny access to the castle gate. As such, spanning large distances was not usually necessary, at least by the drawbridge itself. The still-operational drawbridges at Helmingham Hall are a good example:

The moat is up to 18m wide by 1.8m deep. Each bridge crosses it with three spans — a central 9.6m cast iron span supported on red brick piers, a shorter outer cast iron span of 2.7m, and a timber drawbridge linking the central span to the hall. One of the bridges is wider than the other — the south east bridge is 3.75m between parapets and the north east 2.5m.

The drawbridge construction itself:

The drawbridges span about 2.75m and are without handrails. The south east drawbridge is of oak, with timbers 2.9m wide and 203mm thick. The north east one is similar but a little narrower. They are raised every night and lowered every morning, just as they have been since 1510.

So the drawbridge only reaches out 2.75m(9ft) although the moat was 18m(~60ft) wide.


Update:

I found a reference in an article published in 1867 entitled A Visit to Leeds Castle, to an early drawbridge of exceptional size. The castle at Leeds,in Kent England, had several drawbridges, with one in particular (emphasis mine):

The drawbridge was not only of two arches or rather openings but also of two storeys. In the minister's accounts temp. Edward III it is called the Pons Gloriettae as leading to the tower called the gloriette which now contains the clock &c

I have found no further details concerning actual dimensions, but we can estimate this drawbridge at twice the height of the above-mentioned ones, giving us a span of about 5.5m (18ft).


To address the underlying question of could a 10M long drawbridge be built with 15th century technology, what you are essentially looking for is a wooden beam bridge, once in place. The book A History of Engineering in Classical and Medieval Times, By Donald Hill on page 63 in a discussion of bridges states:

Timber is much weaker then steel, and simple beam bridges are limited to a practical span of about 20 feet"

So 20ft, or 6m appears to be the maximum distance a wooden beam bridge structure could be reasonably be expected to span. This also coincides with the estimate of the size of the drawbridge at Leeds.

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