<P> In early Egyptian pyramids, which were constructed during the Old Kingdom (~ 2600--2500 BCE), the limestone blocks were bound by mortar of mud and clay, or clay and sand . In later Egyptian pyramids, the mortar was made of either gypsum or lime . Gypsum mortar was essentially a mixture of plaster and sand and was quite soft . </P> <P> In the Indian subcontinent, multiple cement types have been observed in the sites of the Indus Valley Civilization, such as the Mohenjo - daro city - settlement that dates to earlier than 2600 BCE . Gypsum cement that was "light grey and contained sand, clay, traces of calcium carbonate, and a high percentage of lime" was used in the construction of wells, drains and on the exteriors of "important looking buildings ." Bitumen mortar was also used at a lower - frequency, including in the Great Bath at Mohenjo - daro . </P> <P> Historically, building with concrete and mortar next appeared in Greece . The excavation of the underground aqueduct of Megara revealed that a reservoir was coated with a pozzolanic mortar 12 mm thick . This aqueduct dates back to c. 500 BCE . Pozzolanic mortar is a lime based mortar, but is made with an additive of volcanic ash that allows it to be hardened underwater; thus it is known as hydraulic cement . The Greeks obtained the volcanic ash from the Greek islands Thira and Nisiros, or from the then Greek colony of Dicaearchia (Pozzuoli) near Naples, Italy . The Romans later improved the use and methods of making what became known as pozzolanic mortar and cement . Even later, the Romans used a mortar without pozzolana using crushed terra cotta, introducing aluminum oxide and silicon dioxide into the mix . This mortar was not as strong as pozzolanic mortar, but, because it was denser, it better resisted penetration by water . </P> <P> Hydraulic mortar was not available in ancient China, possibly due to a lack of volcanic ash . Around 500 CE, sticky rice soup was mixed with slaked lime to make an inorganic − organic composite mortar that had more strength and water resistance than lime mortar . </P>

Motar is made up of what and what