  We show that the ${\cal N}=1$ supergravity theories in ten dimensions with
gauge groups $U(1)^{496}$ and $E_8 \times U(1)^{248}$ are not consistent
quantum theories. Cancellation of anomalies cannot be made compatible with
supersymmetry and abelian gauge invariance. Thus, in ten dimensions all
supersymmetric theories of gravity without known inconsistencies are realized
in string theory.
