Mercury was known to ancient civilizations.
The chemical symbol, Hg, comes from the Latin word "hydragyrum" which means liquid silver, it being the most common liquid metal at room temperature. As a liquid, the metal is extremely mobile and dense and as a solid, it is ductile and malleable (mercury has a melting point of -39C). It is a readily accessible element as it occurs in concentrated ores, mercury (II) oxide being decomposed by heating alone at around 500C (i.e. with no reducing agent), at which temperature mercury distils out. The element and many of its compounds are extremely toxic and, as mercury has a relatively high vapour pressure at room temperature, mercury surfaces should always be kept covered to reduce vapourization.
The use of mercury and its compounds has been reduced due to its toxicity. However, as it acts a "solvent" with most metals where it forms amalgams, it has some use in the field of dental amalgams. It is also used in mercury vapour lamps and many scientific and electrical instruments. One application with which many people will be familiar is the mercury barometer, an instrument used for measuring the pressure of the atmosphere in terms of the height of a column of mercury which exerts an equal pressure.