The horizontal arching mechanism transfers horizontal earth pressures acting on flexible retaining wall panels to neighbouring elements via soil shear stresses. In this research, the horizontal arching mechanism and lateral displacements of fixed cantilever walls are investigated using centrifuge tests. A 300mm high, L-shaped model basement comprising separate but contiguous wall panels of different widths and stiffnesses was built to accommodate this purpose. A series of six tests was carried out at 45 gravities where the panel widths and thicknesses around the model basement were varied, so that the effects of panel geometry and stiffness on horizontal arching could be studied. It is shown that panel crest displacements and base bending moments of the most flexible, narrow panels can be an order of magnitude smaller than conventional active earth pressure calculations would allow.