  The melting transition of the vortex lattice in highly anisotropic, layered
superconductors with commensurate, periodic columnar pins is studied in a
geometry where magnetic field and columnar pins are normal to the layers.
Thermodynamic properties and equilibrium density distributions are obtained
from numerical minimizations of an appropriate free-energy functional. We find
a line of first-order transitions that ends at a critical point as the pin
concentration is increased. A simple Landau theory providing a
semi-quantitative explanation of the numerical results is proposed.
