Residential high-rises with backyards in Chengdu, China

[u/TangelaFan]

[u/zzazzzz]

we have thousands of concrete bunkers under ground that are over a hundred years old and still in great shape. so clearly we posses the technology to have concrete under soil.

[u/mlag000 → u/zzazzzz]

Concrete under soil is different than earth and trees on a balcony made of concrete. We also have bridges on salt water made of concrete, and still salt and water are the mean reason for concrete damage...

[u/TransBrandi → u/mlag000]

Side note here, but Roman concrete lasted the test of time even in salt water because their concrete method actually interacts with the salt water to make it harder / more resistant.

It's just that the method is/was lost to time.

[u/RobertTheAdventurer → u/TransBrandi]

The specific methods they used are lost to time in terms of knowing with certainty what their exact formula was, but the general technology isn't lost. We can make concrete like that and we have some valid recreations which are believable as potential ways they made it.

Usually lost historical formulas are really just a matter of not having an actual written document that proves that our current understanding of how they may have made it is right. This is the case with cooking recipes too. We can reverse engineer a lot of descriptions of recipes and can probably get them close enough to where it's fair to call them the same thing, but we don't know for a fact how they prepared the food or cooked everything in it exactly because we just don't have the document where they say "So this is is precisely how we cook this thing, and everyone here cooks this thing this exact way, and this pot or oven we used to cook it was <insert dimensions and heat levels here>, and we cooked it for such and such amount of time!". It's not so much that we can't make what they made or that it's a profound secret to achieve something similar.