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Four strange places to see London's Roman Wall

(diamondgeezer.blogspot.com)
275 points zeristor | 2 comments | 11 Nov 25 22:31 UTC | HN request time: 0s | source
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tom_alexander ◴[11 Nov 25 23:29 UTC] No.45894350[source]▶
> ground level then was a few metres lower than now

What?! That's huge. What happened?

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pmontra ◴[12 Nov 25 05:37 UTC] No.45896710[source]▶
If you leave ground alone all sort of things grow on it or lay on it. Dirt, mud, leaves etc. Soil grows at about 1 mm per year. 1 meter in 1000 years.

Historically cities were hit by floods and wars and new buildings were built on top of the foundations of old ones. We had an article about that church in Rome built over another roman church built over another roman church, etc. down to an old temple on a spring, or something like that.

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1. asdff ◴[12 Nov 25 06:02 UTC] No.45896831[source]▶
It might even happen faster than that. If I don't sweep my cement patio for about a month, the decaying leaves from the bushes are enough to make about an 1/8th inch of fresh brown soil under the leaf piles.
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2. pmontra ◴[12 Nov 25 07:54 UTC] No.45897444[source]▶
Exactly. This is hard to understand when living in a flat in a modern city but it's immediately clear in any other case.

My figure of 1 mm is about the compacted result of decaying and layering. It may vary a lot according to the configuration of the ground.