The earliest uses of concrete, also known as cement, date back to the Egyptian era. To construct the pyramids, the Egyptians used a mixture of calcinate gypsum, limestone, and clay. Calcinate gypsum is a powder commonly found in plaster. The Romans, who constructed the Coliseum, used lime from heated limestones and mixed it with sand to make mortar. What is the difference between concrete and mortar? Concrete has rocks in it and is used for roads, buildings, and bridges. Whereas mortar, is a bonding agent used between layers of bricks. Concrete used today was invented in 1824 by the English inventor Joseph Aspdin.