The
Third Treaty of San Ildefonso was a treaty between France and Spain in which Spain returned the colonial territory of
Louisiana to France. The treaty was concluded on 1 October 1800 between
Louis Alexandre Berthier representing France and Don
Mariano Luis de Urquijo for Spain. The treaty was negotiated under some duress, as Spain was under pressure from
Napoleon, although Spain did gain the
Tuscany area. The terms of the treaty did not specify the boundaries of the territory being returned, which later became a point of contention between Spain and the United States after the
Louisiana Purchase in 1803, in which France sold its territory to the United States. This treaty also affirmed the earlier
Treaty of Alliance signed at
San Ildefonso on 19 August 1796.