“ SAN ILDEFONSO, Treaty of. A secret treaty between France and Spain, negotiated in October, 1800. France agreed to procure in Italy for the Duke of Parma, the son-in-law of Carlos IV. of Spain, a kingdom which should have a population of from 1,000,000 to 1,200,000, while Spain agreed to retrocede to France, six months after France had carried out her part of the agreement, “the colony or province of Louisiana with the same extent that it had in the hands of Spain and when France owned it, and as it should be according to subsequent treaties between Spain and other powers.” ”