Le Page du Pratz was a French military engineer who came to North America in 1718 and for fifteen years was a planter in Louisiana. During this period he made a five-month tour of the interior of Louisiana. Le Page du Pratz wrote Histoire de la Louisiane in which he drew on information he received from Bourgmont. He also borrowed liberally from the writings of Charlevoix and from Dumont de Montigny’s Mémoires historiques sur la Louisiane (Paris, 1753). Histoire de la Louisiane contained a map entitled “Carte de la Louisiane Colonie Française avec le Cours du Fleuve St. Louis.”
Le Page du Pratz’s map depicts the lower Mississippi and lower Missouri rivers fairly accurately but it mistakenly shows the Missouri River flowing from the west unimpeded by any mountains. This representation was consistent with the widely held belief that the source of the Missouri was near the source of the Rio Grande. Le Page du Pratz estimated the length of the lower Missouri to be nearly 2,400 miles; the actual distance from the mouth of the Missouri to the Three Forks of the Missouri is 2,547 miles.
His map includes Lahontan’s system of rivers and lakes in the North, although it labels the river running westward toward the Pacific the “Beautiful River.” In his book Le Page du Pratz tells of an Indian who discovered a route to the Pacific Ocean via the Beautiful River. The Indian’s path from the Missouri to the Beautiful River is shown on the map. Le Page du Pratz’s book also presents the first published account of Bourgmont’s expedition to the Padouca Indians, or Plains Apaches, in 1724.
“A Map of Louisiana, with the course of the Missisipi” is included in the first English edition of Le Page du Pratz’s book entitled The History of Louisiana (1763). Thomas Jefferson owned this edition of Le Page du Pratz’s work and used it as a reference source as he prepared his treatise on Louisiana. Meriwether Lewis borrowed an English edition of this book from Benjamin Smith Barton, his botany tutor in Philadelphia, and took it on the expedition to the Pacific. Several references to Le Page du Pratz’s work appear in the journals of the expedition. A shorter version of the work entitled “From a Memoir of M. Le Page du Pratz” appeared in Gentleman’s Magazine in 1753.