In the 19th century, the concept for designing metallic structures was to compare the stresses resulting from the loads with a working stress, a fraction of the ultimate strength of the material. The choice of the working stress depended mainly on the experience and theoretical knowledge of designers as early regulations left a lot of discretion to engineers. This paper traces the evolution of French design criteria used in practice for elements made of wrought iron or mild steel, working in tension or compression, based on an extensive survey of the French literature of the 19th century and the beginning of the 20th century. These design criteria are compared with original design reports of train sheds, which show that designers used working stresses higher than recommended in the literature and ensured buckling safety through constructive measures instead of calculations.