The rare earth-rich compounds <i>RE</i>₂₃Rh₇Mg₄ (<i>RE</i> = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction-melting the elements in sealed tantalum tubes. The new compounds were characterized by X-ray powder diffraction. They crystallize with the hexagonal Pr₂₃Ir₇Mg₄ type structure, space group <i>P</i>6₃<i>mc</i>. The structures of La₂₃Rh₇Mg₄ (<i>a</i> = 1019.1(1), <i>c</i> = 2303.7(4) pm, wR2 = 0.0827, 1979 F² values, 69 variables), Nd₂₃Rh₇Mg₄ (<i>a</i> = 995.4(2), <i>c</i> = 2242.3(5) pm, wR2 = 0.0592, 2555 F² values, 74 variables) and Gd₂₃Rh_6.86(5)Mg₄ (<i>a</i> = 980.5(2), <i>c</i> = 2205.9(5) pm, wR2 = 0.0390, 2083 F² values, 71 variables) were refined from single crystal X-ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short <i>RE</i>-Rh distances (283-300 pm in Nd₂₃Rh₇Mg₄). The prisms are condensed via common edges, leading to a rigid three-dimensional network in which isolated Mg₄ tetrahedra (312-317 pm Mg-Mg in Nd₂₃Rh₇Mg₄) are embedded. Temperature dependent magnetic susceptibility data of Ce₂₃Rh₇Mg₄ indicate Curie-Weiss behavior with an experimental magnetic moment of 2.52(1) _B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.Read less <