  A new formulation of theories of supergravity as theories satisfying a
generalized Principle of General Covariance is given. It is a generalization of
the superspace formulation of simple 4D-supergravity of Wess and Zumino and it
is designed to obtain geometric descriptions for the supergravities that
correspond to the super Poincare' algebras of Alekseevsky and Cortes'
classification.
