  We discuss classification of defects of various codimensions within a
holographic model of pure Yang-Mills theories or gauge theories with
fundamental matter. We focus on their role below and above the phase transition
point as well as their weights in the partition function. The general result is
that objects which are stable and heavy in one phase are becoming very light
(tensionless) in the other phase. We argue that the $\theta$ dependence of the
partition function drastically changes at the phase transition point, and
therefore it correlates with stability properties of configurations. Some
possible applications for study the QCD vacuum properties above and below phase
transition are also discussed.
