In the general sense, a cement is any material with adhesive properties. The term cement is also commonly used to refer more specifically to powdered materials which develop strong adhesive qualities when combined with water. These materials are more properly known as hydraulic cements. Gypsum plaster, common lime, hydraulic limes, natural pozzolana and Portland cements are the more common hydraulic cements, with Portland cement being the most important in construction.
Hydraulic cement was first invented by the Egyptians, and later reinvented by the Greeks and Babylonians, who made their mortar out of lime, much harder than the Roman mortars. Later, the Romans produced a good cement from pozzolanic ash.