no [*a priori*]{} reason that distinguishes toroidal compactifications from other ones. A large class of compactifications that received considerable attention in the mid-eighties are compactifications on spheres. These compactifications lead to (maximally supersymmetric) gauged supergravities in lower dimensions [@S7gsugra; @gaugedsu; @DNP]. The latter contain a negative cosmological constant in the action and in many cases admit a stable anti-de Sitter (adS) vacuum. A famous example is the compactification of eleven-dimensional supergravity on $S^7$, which yields [@S7gsugra] $\cn=8$ $adS_4$ gauged supergravity[@N8gaugesugra].

A natural question is what is the rôle of gauged supergravities in M-theory. Since the asymptotic group associated to these theories is different from the one associated to Poincaré supergravities one may consider them as different sectors of M-theory. However, one of the lessons that our experience with dualities teaches us is that differently looking theories may actually be equivalent. Indeed, it has been known for some time that dualities can change the asymptotic geometry of spacetime[@topch]. We have recently[@BPS1] provided a connection between Poincaré and gauged supergravities by giving a set of duality transformations (such duality transformations have also appeared in [@hyun] and were recently also studied in [@berg]) that map solutions of the former to solutions of the 