  The large-scale structure of the Universe has been observed to be
characterized by long filaments, forming polyhedra, with a remarkable 100-200
Mpc periodicity, suggesting a regular network. The introduction of magnetic
fields into the physics of the evolution of structure formation provides some
clues to understanding this unexpected lattice structure. A relativistic
treatment of the evolution of pre-recombination inhomogeneities, including
magnetic fields, is presented to show that equivalent-to-present field
strengths of the order of $10^{-8}$ G could have played an important role.
Primordial magnetic tubes generated at inflation, at scales larger than the
horizon before recombination, could have produced filamentary density
structures, with comoving lengths larger than about 10 Mpc. Structures shorter
than this would have been destroyed by diffusion due to the small
pre-recombination conductivity. If filaments constitute a lattice, the
primordial magnetic field structures that produced the post-recombination
structures of matter, impose several restrictions on the lattice. The simplest
lattice compatible with these restrictions is a network of octahedra contacting
at their vertexes, which is indeed identifiable in the observed distribution of
superclusters.
