Mortar & Roman Concrete

Lime, volcanic ash and aggregate make a building material that carries domes and harbour moles.

The Romans mixed burnt lime with pozzolanic ash and stone chunks to make opus caementicium, which even hardens under water. The Pantheon in Rome (around 126 AD) still has the world's largest unreinforced concrete dome. After the empire ended the knowledge was largely lost until Portland cement replaced it in the 19th century.