  Non-analyticity of QCD with a \theta term at \theta=0 may signal a
spontaneous breaking of both parity and time reversal invariance. We address
this issue by investigating the large volume limit of the topological
susceptibility $\chi$ in pure SU(3) gauge theory. We obtain an upper bound for
the symmetry breaking order parameter <Q> and, as a byproduct, the value
\chi=(173.4(+/- 0.5)(+/- 1.2)(+1.1 / -0.2) MeV)^4 at \beta=6 (a approx= 0.1
fermi). The errors are the statistical error from our data, the one derived
from the value used for \Lambda_L and an estimate of the systematic error
respectively.
