Early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite unpredictable.The ancient Egyptians built the first known dam to exist. The dam was called the Sadd el-Kafara, which in Arabic means "Dam of the Pagans. The dam was 37 ft tall, 348 ft wide at the crest and 265 ft at the bottom.The dam was made of rubble masonry walls on the outsides and filled with 100,000 tons of gravel and stone. A limestone cover was applied to resist erosion and wave action. The structure had no need for cement because the shear weight of the structure was sufficient to ensure stability. The dam failed after a few years and it was concluded that overflow was the cause of failure. The poor workmanship from a hasty construction lead to the failure. The dam was not watertight and water flowed through the structure quickly eroding it away. Once the water overflowed the crest, it quickly eroded away the dam. The dam was a failure and the Egyptians never attempted to build another dam until modern times.The second type of dam known to have been built was an earth dam called Nimrod's Dam in Mesopotamia around 2000 BC. Earth dams are massive dams similar to gravity dams except they are made of soil. The dam is made watertight, with a core wall and filled with an impervious center usually made of clays. Nimrod's dam was built north of Baghdad across the Tigris and was used to prevent erosion and reduce the threat of flooding. The intention was to divert the flow in the river and help irrigate the crops. The dam was built of earth and wood, so it is difficult to be certain of the exact characteristics of the dam.Around 100 AD the Romans were the first civilization to use concrete and mortar in their gravity dams. The dam at Ponte di San Mauro has a great block of concrete among its remains. The evidence indicates that a large slab of concrete was used as the core and the outer layer finished with masonry.Due to the large size and amount of building material need to construct these dams, the arch dam was invented. An arch dam is dependent on its shape for strength, requires less material to build, and is relatively thin. The first known arch dam is Kebar, which was built around 1280 AD in the Mongol period. The limestone dam is located near the ancient town of Quam and stands 85 ft high, 180 ft long at the crest, 16 ft thick at the crest and has a constant radius of curvature of 125 ft. An arch dam needs to be supported by the surrounding geology, the rock formations on either side support the arch.