Ancient civilizations had a high demand for raw materials, like clay, diverse rocks and, most of all, metals. These were required for buildings, crafts, agriculture, their armed forces, financial concerns, art and culture. Clays and rocks produced by opencast mining primarily served for the production of bricks and building blocks, which were used for civil and hydraulic engineering. They were additionally extracted for the manufacture of durable goods and art objects, such as dishes and statues. Metals – like gold, silver, copper, tin, iron and lead – being essential raw materials in antique civilisations, were commonly produced by underground mining. Gold and silver were mostly used as raw material for ancient coins. The use of noble metals in monetary economy has been going on since the seventh century BC, when barter trade was successively replaced by a monetary economy. Copper, tin and iron was mostly produced for the manufacture of arms, whereas lead was, among other things, used for the production of water conduits and as a stain for ornamental painting.