The ancients used 'pozzolan' cement as the paste in their mortar and concrete which enabled civilization to flourish.
"Opus caementiciun' or Roman concrete was invented in the 3rd century BC when builders added a volcanic dust called pozzolana to mortar made of a mixture of lime or gypsum, rocks and water. Pozzolana contained both silica and alumina and created a chemical reaction which strengthened the cohesiveness of the mortar.
The master builders of Rome created many architectural feats out of this material which stand to this day thousands of years later. The knowledge of how to produce pozzolanic cement and concrete was lost after the fall of Rome through the dark ages until it was rediscovered late in the Renaissance.
Modern 'portland' cement
Modern cement is also known as "portland cement" as it was named in a patent in 1824. It is believed that the name refers to its similarity to stone from the Isle of Portland in England.
Cement manufacturers mine and crush materials such as limestone, shale, iron ore, and clay and blend them into a raw feed which is introduced into large rotary cement kilns. After being heated to extremely high ( ~ 2,700 Fahrenheit ) temperatures within the kiln the materials are transformed into small balls of a new material called “clinker” which is cooled and later ground, along with a small quantity of gypsum, to produce the fine gray powder called portland cement.
Cement is to concrete as flour is to cake
Cement is one of the ingredients in the recipe for ready mixed concrete but the two materials are quite different things. The other main ingredients in concrete are fine aggregate (sand), coarse aggregate (rock), and water. Cement mixed with water forms the paste that binds the rest of the ingredients in the recipe for ready mixed concrete together.
Think of cement being to concrete as flour is to cake.
The Colosseum in Rome, Italy illustrates the long history of cement