  Let $(\phi_t)_{t \geq 0}$ be a semigroup of holomorphic functions in the unit
disk $\mathbb{D}$ and $K$ a compact subset of $\mathbb{D}$. We investigate the
conditions under which the backward orbit of $K$ under the semigroup exists.
Subsequently, the geometric characteristics, as well as, potential theoretic
quantities for the backward orbit of $K$ are examined. More specifically,
results are obtained concerning the asymptotic behavior of its hyperbolic area
and diameter, the harmonic measure and the capacity of the condenser that $K$
forms with the unit disk.
