We show that the one dimensional unitary matrix model with potential of the form aU + bU2 + h.c. is integrable. By reduction to the dynamics of the eigenvalues, we establish the integrability of a system of particles in one space dimension in an external potential of the form a cos(x+α) + b cos(2x+ β) and interacting through two-body potentials of the inverse sine square type. This system const...