Pozzolanic material, made from volcanic ash from a specific region of Italy, features prominently. So does lime, and in previous studies it was found that this helps concrete actually grow stronger over time in marine environments like piers. One common inclusion ?" millimeter-sized chunks of white minerals called lime clasts ?" are usually disregarded as a by-product, but in the new study, researchers found that they might be there for a reason. "The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me," said Admir Masic, lead author of the study. "If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story."