  Simplicial lattices provide an elegant framework for discrete spacetimes. The
inherent orthogonality between a simplicial lattice and its circumcentric dual
yields an austere representation of spacetime which provides a conceptually
simple form of Einstein's geometric theory of gravitation. A sufficient
understanding of simplicial spacetimes has been demonstrated in the literature
for spacetimes devoid of all non-gravitational sources. However, this
understanding has not been adequately extended to non-vacuum spacetime models.
Consequently, a deep understanding of the diffeomorphic structure of the
discrete theory is lacking. Conservation laws and symmetry properties are
attractive starting points for coupling matter with the lattice. We present a
simplicial form of the contracted Bianchi identity which is based on the E.
Cartan moment of rotation operator. This identity manifests itself in the
conceptually-simple form of a Kirchhoff-like conservation law. This
conservation law enables one to extend Regge Calculus to non-vacuum spacetimes
and provides a deeper understanding of the simplicial diffeomorphism group.
