With the development of the curtain wall in the mid nineteenth century when traditionally load bearing walls were replaced by the development and widespread use of structural concrete and later reinforced concrete thus facilitaing that the the exterior walls of buildings were no longer required for structural support. The exterior walls could be much lighter and more open than the load bearing walls of the past. This gave way to the increased use of glass as an exterior facade and the modern day curtain wall was born. Extal's curtain wall systems employ the very latest in innovation and design technology within this field.