Abstract: The outer metallic stairway, particularly made of aluminium, for multistage buildings or buildings of a rather important height, to be used for allowing the occupants of a multistage building to evacuate this one is essentially fixed and supported by means of four uprights forming a column of support that are mounted vertically in a square or rectangular arrangement, the flights of stairs being fixed to at least two of the sides of the support column, the uprights being connected to one another at different levels and at least on the level of the landings by means of four horizontal tie-bars, one of which on a level with a story landing being extended beyond a second upright for supporting said landing on a whole side or to be fixed to an existing landing and to support the flight of stairs fixed to it that descends from said landing, and two of the four tie-bars that are provided on the level of an intermediate landing being extended beyond one of the uprights in order to form a part of the supporting frame