  EAS arrays are survey instruments able to monitor continuously all the
overhead sky. Their sensitivity in the sub-TeV/TeV energy domain cannot compete
with that of Cherenkov telescopes, but the wide field of view (about 2 sr) is
ideal to complement directional detectors by performing unbiased sky surveys,
by monitoring variable or flaring sources such as Active Galactic Nuclei (AGN)
and to discover transients or explosive events (GRBs). Arrays are well suited
to study extended sources, such as the Galactic diffuse emission, and to
measure the spectra of Galactic sources at the highest energies (near or beyond
100 TeV). An EAS array is able to detect at the same time events induced by
photons and charged cosmic rays, thus studying the connection between these two
messengers of the non-thermal Universe. Therefore, these detectors are, by
definition, multi-messenger instruments. All EAS arrays presently in operation
or under installation are located in the Northern hemisphere. The scientific
potential of a next-generation survey instrument in the Southern Hemisphere
will be presented and briefly discussed.
