  We complete a metric-free axiomatic framework for electrodynamics by
introducing the appropriate energy-momentum current Sigma of the
electromagnetic field. We start from the Lorentz force density and motivate the
form of Sigma. Then we postulate it (fourth axiom) and discuss its properties.
In particular, it is found that Sigma is traceless and invariant under an
electric-magnetic reciprocity transformation. By using the Maxwell-Lorentz
spacetime relation (fifth axiom), Sigma is also shown to be symmetric, that is,
it has 9 independent components
