  We say that a Riemannian manifold M has rank at least k if every geodesic in
M admits at least k parallel Jacobi fields. The Rank Rigidity Theorem of
Ballmann and Burns-Spatzier, later generalized by Eberlein-Heber, states that a
complete, irreducible, simply connected Riemannian manifold M of rank at least
2 (the higher rank assumption), whose isometry group satisfies the condition
that the recurrent vectors are dense in the unit tangent bundle SM (the duality
condition), is a symmetric space of noncompact type. This includes, for
example, higher rank M which admit a finite volume quotient. We adapt the
method of Ballmann and Eberlein-Heber to prove a generalization of this theorem
where the manifold M is assumed only to have no focal points. We then use this
theorem to generalize to no focal points a result of Ballmann-Eberlein stating
that for compact manifolds of nonpositive curvature, rank is an invariant of
the fundamental group.
