  We present a succinct formulation of the energy-momentum tensor of the Glasma
characterizing the initial color fields in relativistic heavy-ion collisions in
the Color Glass Condensate effective theory. We derive concise expressions for
the (3+1)D dynamical evolution of symmetric nuclear collisions in the weak
field approximation employing a generalized McLerran-Venugopalan model with
non-trivial longitudinal correlations. Utilizing Monte Carlo integration, we
calculate in unprecedented detail non-trivial rapidity profiles of early-time
observables at RHIC and LHC energies, including transverse energy densities and
eccentricities. For our setup with broken boost invariance, we carefully
discuss the placement of the origin of the Milne frame and interpret the
components of the energy-momentum tensor. We find longitudinal flow that
deviates from standard Bjorken flow in the (3+1)D case and provide a geometric
interpretation of this effect. Furthermore, we observe a universal shape in the
flanks of the rapidity profiles regardless of collision energy and predict that
limiting fragmentation should also hold at LHC energies.
