Let me tell you about concrete.
As difficult as it is to believe, the concrete we have today isn't as good as the extremely sophisticated pozzolan geopolymer the Romans developed two millennia ago.
Stronger and ridiculously more durable than modern science is capable of producing, the recipe for Roman concrete has been lost to time and efforts to reverse-engineer it have largely failed.
The Romans built structures with concrete we are simply incapable of reproducing. And even if we could, they wouldn't last as long.
One of these structures is the rotunda of the Pantheon
. Built 1,900 years ago during the rule of the emperor Hadrian
, it remains the largest unreinforced concrete dome in the world. The exterior is encased in brick which has an unusual and distinctive colour.