  A description of how a theory of gravity can be considered as a gauge theory
(in the sense of Trautman) of the Poincare' group is given. As a result, it is
shown that a gauge theory of this kind is consistent with the Equivalence
Principle only if the Lagrangian and the constraints are preserved not only by
the gauge transformations but also by an additional family of transformations,
called "pseudo-translations". Explicit expressions of pseudo-translations and
of their action on gravitational gauge fields are given. They are expected to
be useful for geometric interpretations of their analogues in supergravity
theories.
