It was discovered that limestone, when burnt and combined with water, produced a material that would harden with age. The earliest documented use of lime as a construction material was approximately 4000 B.C. when it was used in Egypt for plastering the pyramids(ref. ii). The beginning of the use of lime in mortars is not clear. It is well documented, however, that the Roman Empire used lime based mortars extensively. Vitruvius, a Roman architect, provided basic guidelines for lime mortar.The most significant developments in the use of pozzolans in mortars occurred in the 18th century. It was discovered that burning limestone containing clays would produce a hydraulic product. In 1756, James Smeaton developed perhaps the first hydraulic lime product by calcining Blue Lias limestone containing clay. An Italian pozzolanic earth from Civita Vecchia was also added to provide additional strength(ref. v). This mortar mixture was used to build the Eddystone Lighthouse. James Parker patented a product called Roman cement or natural cement in 1796. Natural cement was produced by burning a mixture of limestone and clay together in kilns similar to those used for lime. The resulting product was ground and stored in waterproof containers. Typically, natural cements had higher clay contents than hydraulic lime products, which allowed for better strength development. Natural cement mortar was used in construction where masonry was subjected to moisture and high levels of strength were needed