High-resolution x-ray powder-diffraction experiments were performed on europium metal at high pressure up to 50GPa. At variance with previous reports, the hcp phase of Eu was observed to be stable not only to 18GPa, but to 31.5GPa. At 31.5(5)GPa, europium transforms to a phase (Eu-IV) with an incommensurately modulated monoclinic crystal structure with superspace group C2/c(q_{1}0q_{3})00. This new phase was observed to be stable to 37.0GPa, where another phase transition was observed. Eu-IV is the first phase in the lanthanide elements with an incommensurate crystal structure.