  The asymptotic behaviour of the vacuum energy density, ${\bar E}(\theta)$, at
$\theta \ra \pm i \infty$ is found out. A new interpretation and a qualitative
discussion of the ${\bar E}(\theta)$ behaviour are presented. It is emphasized
that the vacuum is doubly degenerate at $\theta=\pi$, and the quark electric
string can terminate on the domain wall interpolating between these two vacua.
The potential of the monopole field condensing in the Yang-Mills vacuum is
obtained.
