Wiki : Pozzolana

Puzzolana mortar (puzolan harcı) was composed of
puzzolana85 and lime. It quickly hardened under water. In fact, this material (also called
‘Roman cement’) had long been used widely in underwater construction before the
introduction of cement (Aksoy 1982, 73), especially in European hydraulic architecture
during the eighteenth century (Merino 1985, 47).