  The gravitational interaction of (classical and quantum) spinning bodies is
currently the focus of many works using a variety of approaches. This note is a
comment on a short paper by Jean-Marie Souriau, now reprinted in the GRG Golden
Oldies collection. Souriau's short 1970 note was a pioneering contribution to a
symplectic description of the dynamics of spinning particles in general
relativity which remained somewhat unnoticed. We explain the specificity of
Souriau's approach and emphasize its potential interest within the current
flurry of activity on the gravitational interaction of spinning particles.
