The study of groups originally grew out of an understanding of permutation groups. Permutations had themselves been intensively studied by Lagrange in 1770 in his work on the algebraic solutions of polynomial equations. This subject flourished and by the mid 19th century a well-developed theory of permutation groups existed, codified by Camille Jordan in his book "Traité des Substitutions et des Équations Algébriques" of 1870. Jordan's book was, in turn, based on the papers that were left by Évariste Galois in 1832.