> Is it because we have lost the secrets of ancient Roman technology?

> Not really. We know how to make durable concrete; it’s just more expensive than the alternatives that last 30-40 years.

... For a span of almost 2000 years this was not the case, there was nobody you could pay to make a concrete dome like the Pantheon's, not at any price. And we only properly reverse-engineered the Roman recipe in the past decade.

I think a technology still counts as "lost" even if it gets rediscovered in the distant future!