In this paper, it is proved that Saint-Venant's solution for torsion can be obtained from the following simplified assumptions: (?τxz)/(?z)=(?τyz)/(?z)=0. These assumptions are much more simplified than those given by Saint-Venant in 1855, A. Clebsch in 1862, W. Voigt in 1887, and J. N. Goodier in 1937.