Where is (or was) the biggest medieval drawbridge?

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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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