In a reinvestigation of the phase relations within the section CeSi 2 –Al at 600 and 500°C, two new compounds were found: CeAlSi 2 and Ce 3 Al 4 Si 6 . The crystal structures were solved from X-ray powder diffraction data employing Patterson and difference Fourier syntheses followed by full-matrix full-profile Rietveld refinement. Both compounds crystallize with new trigonal structure types as follows. CeAlSi 2 :P3m1,Z= 2,a= 0.41707(1) nm,c= 1.12147(2) nm,R I = 0.077,R F = 0.050. Ce occupies the 2c site withz= 0.1855(1), Si is in the 2d sites withz 1 = 0 andz 2 = 0.3525(5), and Al is in the 2d site withz= 0.5901(6). Ce 3 Al 4 Si 6 :P3m1,Z= 1,a= 0.41887(1) nm,c= 1.81202(6) nm,R I = 0.065,R F = 0.035. Ce occupies the 1b site and the 2c site withz= 0.1149(1); Si is in the 2d sites withz 1 = 0,z 2 = 0.2198(9), andz 3 = 0.6096(6); Al is in the 2d sites withz 1 = 0.3564(8) andz 2 = 0.752(1). Both structures combine structural units of the AlB 2 type, CeSi 2 (m), and of the La 2 O 3 type, CeAl 2 Si 2 (n), and form a structural seriesRE m+n Al 2 n Si 2m+2n with CeAlSi 2 (m= 1,n= 1) and Ce 3 Al 4 Si 6 (m= 1,n= 2) as two early representatives of the series.