  Phase transitions of systems confined in long cylindrical pores (capillary
condensation, wetting, crystallization, etc.) are intrinsically not sharply
defined but rounded. The finite size of the cross section causes destruction of
long range order along the pore axis by spontaneous nucleation of domain walls.
This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa
model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted
by a phenomenological theory. We show that characteristic differences between
the behavior of pores of finite length and infinitely long pores occur. In
pores of finite length a rounded transition occurs first, from phase
coexistence between two states towards a multi-domain configuration. A second
transition to the axially homogeneous phase follows near pore criticality.
