Although the Romans are generally credited as being the first concrete engineers, a form of concrete, utilizing lime, dating to 6500 B.C. has been discovered by archaeologists in Syria. Other early forms of concrete have been discovered along the banks of the Danube River in Yugoslavia, dating to about 5600 B.C., and in Egypt, dating to around 2500 B.C. Around 600 B.C., the Greeks discovered a natural Pozzolan on Santorini Island that developed hydraulic properties when mixed with lime. The first examples of Roman concrete date to 300 B.C. A concrete made with pozzolanic, hydraulic cement, developed by the Romans in 75 B.C. was used in building the theater at Pompeii and the Roman baths. Both the Colosseum and the Pantheon contain large amounts of concrete. There was an attempt by Roman engineers to use bronze rods to reinforce concrete, but this failed because bronze had a higher rate of expansion than concrete. After the fall of the Roman Empire, the use of pozzolan technology was forgotten for the next 1,300 years. In Britain, the Saxons did limited work with concrete, but the Norman invasion of 1066 brought more sophisticated concrete technology. In 1756, engineer John Smeaton was commissioned to build a new lighthouse on the Eddystone rocks in the English Channel. Smeaton elected to use stone rather than timber, but needed a better mortar than anything available at the time. He found this mortar when he combined burnt Aberthaw blue lias, a limestone from South Wales, and an Italian pozzolan from Civitavecchia. In 1796, Rev. James Parker of Northfleet patented what he called Roman cement, which he believed to be the reincarnation of the Roman cement of ancient times. This cement remained popular until the middle of the 19th century and was used in the first tunnel under a navigable river.