  We consider self-gravitating fluids in cosmological spacetimes with Gowdy
symmetry on the torus $T^3$ and, in this class, we solve the singular initial
value problem for the Einstein-Euler system of general relativity, when an
initial data set is prescribed on the hypersurface of singularity. We specify
initial conditions for the geometric and matter variables and identify the
asymptotic behavior of these variables near the cosmological singularity. Our
analysis of this class of nonlinear and singular partial differential equations
exhibits a condition on the sound speed, which leads us to the notion of
sub-critical, critical, and super-critical regimes. Solutions to the
Einstein-Euler systems when the fluid is governed by a linear equation of state
are constructed in the first two regimes, while additional difficulties arise
in the latter one. All previous studies on inhomogeneous spacetimes concerned
vacuum cosmological spacetimes only.
