  We revisit the relativistic coupling between gravity and electromagnetism,
putting particularly into question the status of the latter; whether it behaves
as a source or as a form of gravity on large scales. Considering a
metric-affine framework and a simple action principle, we find out that a
component of gravity, the so-called homothetic curvature field, satisfies both
sets of Maxwell equations. Therefore, we arrive at a gravito-electromagnetic
equivalence analogous to the mass-energy equivalence. We raise and discuss some
crucial questions implied by the aforementioned finding, refreshing our
viewpoint of electromagnetism in curved spacetime.
