Roman concrete

Most of us have had the opportunity to look at, even touch, Roman mortar. At http://news.discovery.com/history/roman-concrete-mimicked-resistant-volc… … Roman concrete closely resembles rock found in the depths of a dormant volcano in Italy and researchers say they tried to reproduce the rock artificially as it was so strong and durable. Roman concrete has withstood 2000 years of erosion and exploitation and the walls of buildings can still be seen (at Silchester and St Albans for example) – stumps of walls as most the stone has been reused in medieval buildings (such as churches and abbeys etc).