On a simply connected negatively curved manifold, the horospheres are spheres centered at a point at infinity. They also are the projections of the strong (un)-stable leaves of the (un)-stable foliation of the geodesic flow. We will study relations between their dynamical and geometrical aspects and show: the horospheres of a closed negatively curved manifold of dimension at least three is hyperbolic if and only if the horospheres are isometric to the euclidean space.