Isn’t this no longer true? I’ve seen many experimental archaeology documentaries that use a recipe that uses pozzolanic ash and rock from volcanoes in Italy that they show to create the same properties found in Roman concrete. We don’t make concrete with it now because the supply is too limited and the expense of mining it would be greater than making portland cement.
Every civilisation for the last million years has categorised itself thus, and, yet, here we are without their technology.
We still don't know how the Romans made a concrete that is as durable as it is (and nothing we have is nearly as good)