Episodes of slow and fast plate subduction, slab rollback, and backarc opening are widely documented; e.g., in the central Mediterranean region. Pervasive damage by fluids is emerging as a possible weakening mechanism that could lead to slab segmentation and breakoff. We show that low-velocity anomalies within the Ionian slab present in along-dip seismic tomography profiles are traces of past damaging events generated by water penetration into the oceanic lithosphere when it was at the trench. We propose that the stepwise evolution of the central Mediterranean over the past 21 m.y. has been governed by strength changes of the Ionian slab induced by damage. More generally, we speculate that the cyclicity of such a process in space and time in the different circum-Mediterranean subduction events may have led to the present shape of the Mediterranean basin.