  We show that the first-order D=4, N=1 pure supergravity lagrangian four-form
can be obtained geometrically as a quadratic expression in the curvatures of
the Maxwell superalgebra. This is achieved by noticing that the relative
coefficient between the two terms of the Lagrangian that makes the action
locally supersymmetric also determines trivial field equations for the gauge
fields associated with the extra generators of the Maxwell superalgebra. Along
the way, a convenient geometric procedure to check the local supersymmetry of a
class of lagrangians is developed.
