[en] An analysis of three-pion-production data at 23 GeV/c is described; these reactions are of the form π^-A → π⁺π^-π^-A where A is one of the nuclear targets: carbon, aluminum, copper, silver, or lead. Total and differential cross sections are quoted, and the method of their computation is outlined. The spin--parity composition of the three-pion system has been analyzed using the Illinois method of partial wave analysis. The partial wave structure of the data is remarkably similar to that of the data from hydrogen, except for the distributions in momentum transfer, which exhibit the usual coherent and incoherent contributions of nuclear scattering. The partial-wave results were fitted with an optical model for three-pion production, with very good results. With this model the absorptions of the three-pion system (in nuclear matter) turn out to be roughly equal to that of a single pion, 25 millibarns, except for the J/sup p/ = 0^- component of the production, which is roughly 50 millibarns. In particular, the A₂ (J/sup p/ = 2⁺, mass = 1310 MeV) is coherently produced, with an absorption of roughly 25 millibarns