A rotor of a rotorcraft provided with a plurality of lift assemblies and with a drive system for driving said lift assemblies in rotation about an axis of rotation, said drive system including a hub which is mobile solely in rotation about said axis of rotation, each lift assembly having a retention and mobility member connected to the hub in order to articulate the lift assembly to the hub about three directions of rotation (D1, D2, D3), said rotor having one abutment mechanism per lift assembly for limiting the flapping movement of the lift assembly upwards and downwards under predetermined conditions, each abutment mechanism of a lift assembly comprising: - an abutment projection integral with said lift assembly, each abutment projection comprising an abutment end provided with an inner face facing said drive system and with an outer face opposite said inner face, - at least one lever pivoting about a pivot shaft integral with the drive system, each lever extending longitudinally from a fly weight to a hook which defines a blind groove suitable for longitudinally surrounding said abutment end in an engagement position and for releasing this abutment end in a disengagement position obtained under the effect of centrifugal force, said hook being provided with two walls in elevation (53, 54) rising from a bottom wall and forming a J-shaped periphery which defines said groove, one of said walls in elevation being referred to as "first wall in elevation" and the other wall in elevation being referred to as "second wall in elevation", said second wall in elevation comprising a lower bearing zone for blocking said outer face following upward flapping of the lift assembly, - a return means acting on said lever for tending to position it in the engagement position, said rotorcraft rotor being characterised in that said first wall in elevation comprises an upper bearing zone for blocking said inner face following downward flapping of the lift assembly, said upper bearing zone being present in an upper horizontal plane directly above a lower horizontal plane passing through the lower bearing zone. - an abutment projection integral with said lift assembly, each abutment projection comprising an abutment end provided with an inner face facing said drive system and with an outer face opposite said inner face, - at least one lever pivoting about a pivot shaft integral with the drive system, each lever extending longitudinally from a fly weight to a hook which defines a blind groove suitable for longitudinally surrounding said abutment end in an engagement position and for releasing this abutment end in a disengagement position obtained under the effect of centrifugal force, said hook being provided with two walls in elevation (53, 54) rising from a bottom wall and forming a J-shaped periphery which defines said groove, one of said walls in elevation being referred to as "first wall in elevation" and the other wall in elevation being referred to as "second wall in elevation", said second wall in elevation comprising a lower bearing zone for blocking said outer face following upward flapping of the lift assembly, - a return means acting on said lever for tending to position it in the engagement position,