  While current atmospheric Cherenkov installations consist of only a few
telescopes each, future installations will be far more complex. Monte Carlo
simulations have become an essential tool for the design and optimisation of
such installations. The CORSIKA air-shower simulation code and the sim_telarray
code for simulation of arrays of Cherenkov telescopes have been used to
simulate several candidate configurations of the future Cherenkov Telescope
Array (CTA) in detail. Together with other detailed and simplified simulations
the resulting data provide the basis for the ongoing optimisation of CTA over a
wide energy range. In this paper, the simulation methods are outlined and
preliminary results on a number of configurations are presented. It is
demonstrated that the initial goals of the CTA project can be achieved with
available technology, at least in the medium and high energy range (about 100
GeV to 100 TeV).
