Third Treaty of San Ildefonso

The Third Treaty of San Ildefonso was a secret agreement signed on October 1, 1800 between Spain and the French Republic, negotiated by General Alexandre Berthier for France and Mariano Luis de Urquijo for Spain. By it Spain agreed in principle to retrocede its North American colony of Louisiana to France, in return for France enlarging the Italian domains of the Duke of Parma, a son-in-law of the Spanish king, which could take in Tuscany. Spain also promised six ships of the line, and the parties reaffirmed the alliance made at San Ildefonso in 1796. The terms were later confirmed by the March 1801 Treaty of Aranjuez, and Spain transferred Louisiana to France in 1802. Because France later sold Louisiana to the United States in 1803, the agreement is seen as a step toward the Louisiana Purchase.