  We investigate the caustic structure of a lens composed by a discrete number
of point-masses, having mutual distances smaller than the Einstein radius of
the total mass of the system. Along with the main critical curve, it is known
that the lens map is characterized by secondary critical curves producing small
caustics far from the lens system. By exploiting perturbative methods, we
derive the number, the position, the shape, the cusps and the area of these
caustics for an arbitrary number of close multiple lenses. Very interesting
geometries are created in some particular cases. Finally we review the binary
lens case where our formulae assume a simple form.
