[riddlemethat]

I've read that ancient Roman concrete was manufactured in a way that is seemingly lost to time. It's also practically impervious to the elements.

http://www.romanconcrete.com/docs/spillway/spillway.htm

If we want to find a way to build beneath the sea that's a good place to start.

[mintplant]

According to this article, a 2013 study successfully reverse-engineered the recipe for Roman concrete:

http://www.ancient-origins.net/news-history-archaeology/rese...

[ChuckMcM]

That is an awesome link. Thanks for that.