  The pre-melting of high vortex density planes observed recently in layered
superconductors in tilted magnetic field is explained theoretically. Based on
the structural information of the crossing lattices of pancake and Josephson
vortices the effective vortex cage potential at different lattice sites is
determined numerically. Melting takes place when the thermal energy allows
proliferation of vacancy-interstitial pairs. It is found that the increased
density of pancake vortex stacks in the planes containing Josephson vortices,
rather than their incommensurate structure, is the main cause for pre-melting.
