  STREGA (STRucture and Evolution of the GAlaxy) is a Guaranteed Time survey
being performed at the VST (the ESO VLT Survey Telescope) to map about 150
square degrees in the Galactic halo, in order to constrain the mechanisms of
galactic formation and evolution. The survey is built as a five-year project,
organized in two parts: a core program to explore the surrounding regions of
selected stellar systems and a second complementary part to map the southern
portion of the Fornax orbit and extend the observations of the core program.
The adopted stellar tracers are mainly variable stars (RR~Lyraes and Long
Period Variables) and Main Sequence Turn-off stars for which observations in
the g,r,i bands are obtained. We present an overview of the survey and some
preliminary results for three observing runs that have been completed. For the
region centered on $\omega$~Cen (37 deg^2), covering about three tidal radii,
we also discuss the detected stellar density radial profile and angular
distribution, leading to the identification of extratidal cluster stars. We
also conclude that the cluster tidal radius is about 1.2 deg, in agreement with
values in the literature based on the Wilson model.
