The title of this article is redundant since all mathematical theories of electromagnetism are relativistic. Indeed, as Einstein wrote, "The special theory of relativity... was simply a systematic development of the electrodynamics of Clerk Maxwell and Lorentz". Combination of spatial and temporal variables in Maxwell's theory required admission of a four-manifold. Finite light speed and other constant motion lines were described with analytic geometry. Orthogonality of electric and magnetic vector fields in space was extended by hyperbolic orthogonality for the temporal factor.