Construction material made from clay mixed with temper such as straw. Initially hand-modelled during the Neolithic Age and then moulded in quadrangular forms, bricks were the most common construction material in Mesopotamia, and were used for building until fairly recently. They were either sun-dried adobe, or kiln-fired bricks, of which the first date to the 3rd millennium in Mesopotamia but only came into widespread use as building materials from the 1st millennium BCE. Relief brick decorations appeared as early as the 2nd millennium but were chiefly used in the 1st millennium BCE. Some were enamelled by covering pre-fired bricks with a liquid glaze which were then vitrified when fired a second time. Different colours were obtained using metal oxides.