Take a stroll through the ancient ruins of the Romans, Egyptians, Persians, and the Assyrians, you may notice something odd about their concrete structures. Despite being thousands of years old, they seem to be withstanding the ravages of time much better than our modern concrete counterparts. The reason for this phenomenon is found in the concrete used by the ancients. It was clearly superior to the kind we use. So why don’t we use the same kind? We would, except for the embarrassing little problem that we seem to have lost the recipe.

The success of the Roman Empire had much to do with the fact that Romans were the original Borg of Star Trek fame. They not only conquered, but they assimilated the technology of those whom they subdued. In the course of conquering most of the Western world, they came across a method for making concrete that would last for millennia. They carried this technology with them as the empire expanded, so that by the beginning of the fifth century, concrete marvels could be found throughout the Roman world.

The Roman Empire ended in A.D. 476. In its ruin, it left behind its concrete constructions, but the method for making the concrete was lost. Nearly 1,500 years would pass before our modern method of making concrete was discovered. This is one situation where “new” does not equate to “improved.” Modern concrete — known as Portland cement — somehow lacks the properties of its Roman counterpart that allows the ancient structures to expand and contract without cracking and deteriorating.

Scientists have recently concluded that Roman concrete owes much of its durability to the use of volcanic ash. This not only gives it better strength but it also better protects it from salt water erosion. The precise method of replicating the classical concrete, however, remains lost to the ages.

Read more fun facts about the Roman Empire.

Read more fun facts about engineering.