The phases and phase transitions of solid xenon monolayers on a graphite single crystal were investigated using high-resolution synchrotron x-ray scattering. As the temperature is lowered a sequence of incommensurate solid phases (aligned'rotated'reentrant aligned) occurs. This sequence is followed by an incommensurate-commensurate transition. Zero-temperature mean-field theories are able to explain the C-IC transition but not the reentrant rotational transitions. The corrugation of the adsorption potential and the width of domain walls are estimated using relaxation simulations at zero temperature. © 1989 The American Physical Society.