  We give a spinorial construction of Sasakian and 3-Sasakian structures in
arbitrary dimension, generalizing previously known results in dimensions 5 and
7. Furthermore, we obtain a complete description of the space of invariant
spinors on a homogeneous 3-Sasakian space, and show that it is spanned by the
Clifford products of invariant differential forms with a certain invariant
Killing spinor. Finally, we give a basis for the space of invariant Riemannian
Killing spinors on a homogeneous 3-Sasakian space, and determine which of these
induce the homogeneous 3-Sasakian structure.
