system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How did the secret to concrete get "lost" when the Western Roman Empire fell?

Was there not a single engineer or architect who fled the doomed WRE into the ERE? Or was it a closely guarded secret kept only in Rome itself and was lost when the city was sacked. I just can't understand how something like that is lost when half the Empire kept existing for a thousand years.
gpt
The first thing here is that the Romans did not have some super secrete concrete recipe. They built a vast amount of structures using a bunch of different concretes. By chance, some of them were quite strong and the buildings remain, and some were failures. But we don't see those anymore, so many assume they never existed. Because it was just another in hundreds of concrete recipes, we don't have the exact formulation for the ones that remained standing.