  Domain wall networks in the early universe, formed upon spontaneous breaking
of a discrete symmetry, have a rich impact on cosmology. Yet, they remain
somewhat unexplored. We introduce a new analytic strategy to understand better
the domain wall epoch, from formation to annihilation. Our method includes a
quantum field theoretical treatment of the initial state at domain wall
formation, as well as of the time evolution. We find that the domain wall area
density for a network with biased initial condition in $d+1$ dimensional flat
spacetime evolves as $t^{-1/2}\,\exp\big(- (t/t_{ann})^{d/2}\big)$. We comment
on the relation between this and previous results obtained in condensed matter
and in cosmology. The extrapolation of this law to an expanding universe
applies to networks that are close to the domain wall `gas' limit.
