The ternary system CsCl−NaCl−LaCl3 was investigated by means of differential thermal analysis and X-ray powder diffraction analysis. There exists one congruently melting compound, Cs2NaLaCl6, crystallizing with the cubic elpasolite structure. No quasi-binary section exists for the whole system, however three binaries range from the ternary compound Cs2NaLaCl6 to NaCl, CsLa2Cl7 and Cs3LaCl6 resp., dividing the system in three areas of composition: one triangle, Cs3LaCl6−Cs2NaLaCl6−CsLa2Cl7, containing additionally a compound Cs2LaCl5 below 510°C, and the two areas CsCl−NaCl−Cs2NaLaCl6−Cs3LaCl6 and Cs2NaLaCl6−NaCl−LaCl3−CsLa2Cl7, containing a mixed crystal range between LaCl3 and Na3La5Cl18. These areas could be further divided in five triangles, so that the whole system contains six Alkemade triangles.