  We present a calculation of the lowest-lying baryon masses in the quenched
approximation to QCD. The calculations are performed using a non-perturbatively
improved clover fermion action, and a splitting is found between the masses of
the nucleon and its parity partner. An analysis of the mass of the first radial
excitation of the nucleon finds a value considerably larger than that of the
parity partner of the nucleon, and thus little evidence for the Roper resonance
as a simple three-quark state
