I found this article and short video about Roman concrete that I'd like to share. Modern Concrete Ancient Roman Concrete From article: Ancient Rome Concrete Mystery Solved by Scientists | Time Modern cement mixtures tend to erode, particularly in the presence of seawater, but the Roman recipe of volcanic ash, lime, seawater and a mineral called aluminium tobermorite actually reinforces the concrete and prevents cracks from expanding, researchers found. The reaction was caused by the seawater continually ramming into the structures for hundreds of years, allowing the mineral mixture of silica oxides and lime to grow between the volcanic rock aggregate and mortar to develop resistance. “Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” lead author Marie Jackson from the University of Utah said in the journal.