  Canonical quantisation of rigid particles is considered paying special
attention to the restriction on phase space due to causal propagation. A mixed
Lorentz-gravitational anomaly is found in the commutator of Lorentz boosts with
world-line reparametrisations. The subspace of gauge invariant physical states
is therefore not invariant under Lorentz transformations. The analysis applies
for an arbitrary extrinsic curvature dependence with the exception of only one
case to be studied separately. Consequences for rigid strings are also
discussed.
