Before the 1670s, European cartographers had only a very vague knowledge of the lands north of the Gulf of Mexico, as their geography was particularly dependent on Spanish travel narratives.
 
The merchant Louis Jolliet and the Jesuit Jacques Marquette were the first Frenchmen to leave behind written testimony of an expedition on the river (1673). They had heard about the Mississippi from Indigenous people, but they remained uncertain about its orientation and the position of its mouth – ambiguities best resolved by navigating it themselves. For the Jesuit, a successful expedition would mean encountering many new Indigenous peoples to convert; for the merchant, it offered the promise of new markets for European products. Accustomed to travel and forest life, Jolliet and Marquette possessed the necessary knowledge to make a cartographic record of the territories they crossed. Their journals demonstrate how they relied on Indigenous knowledge to plan their route between the Great Lakes and the Mississippi. The few maps that emerged from their expedition reveal the colony’s interest in this vast space to the southeast of Canada: they show a multitude of villages hitherto unknown to the French, as well as particularly enticing deposits of minerals.
 
Other Canadian merchants were also interested in the Mississippi and its commercial potential. This was the case with René-Robert Cavelier de La Salle, who traveled down the river and reached its mouth in April 1682. In an attempt to obtain financial support from King Louis XIV for his colonization and commercial projects, La Salle and his partners coined a new name for the territory irrigated by the Mississippi: Louisiana, in homage to the King. More maps were produced, showing the course of the river as far as its mouth. It is possible that La Salle intentionally falsified the maps, bringing the Mississippi closer to the mines of New Mexico, to attract greater interest from the decision-makers at the court of Versailles. The explorer was persuasive, for, the following year, with royal support, he led a convoy of ships from France to the Gulf of Mexico to establish a colony there. But he failed to find the mouth of the river by sea, it being well-hidden by marshes and wrongly placed on the maps.
 
Later, at the end of the 17th century, Pierre Le Moyne d’Iberville from Montreal was commissioned to continue the exploration of the Mississippi and resuscitate the colonization program. Resulting maps of the land around the Mississippi reflect the knowledge that had been acquired from Indigenous people about the territories along the coast and in the hinterland. In Paris, the geographer Guillaume Delisle was one of those who quickly obtained updated data about this region, in particular about the longitude of the Mississippi. Updated maps were in high demand as the Compagnie d’Occident, subsequently responsible for the development of Louisiana, orchestrated a promotional campaign in 1718 that included cartographic material. It was at this time that Delisle drew his Carte de la Louisiane et du cours du Mississippi, influenced in particular by the memoirs and maps of the priest François Le Maire. Delisle’s map features many Mississippi tributaries, especially the Missouri River, a possible route to the Pacific Ocean.
 
After New Orleans was founded and made the seat of the colonial administration in 1718, the Mississippi River (which was also called the Saint-Louis River) gained importance for naval officers and the engineers and draftsmen of the Compagnie des Indes. The latter managed most colonial development via the construction of forts, the delimitation of concessions, and the reconnaissance and surveying of important water courses, both by using compass readings and by measuring time and location to calculate distance traveled (relevé à l’estime). They conducted various surveys of different sections of the river, from its mouth all the way to the Illinois Country, far upstream.
 
In 1719, the officer Bernard Diron d’Artaguiette made a compass-based survey of the Mississippi River from New Orleans to the Illinois Country. He calculated that, following all the river’s detours, he had traveled 400 leagues. In the 1720s, while attempts to make the river accessible to ships and to protect New Orleans were in progress, engineer Adrien de Pauger made several maps of the Mississippi delta. In 1721, 1726 and 1731, engineer Ignace-François Broutin surveyed the Mississippi using relevés à l’estime between New Orleans and the lands of the Natchez, where he commanded Fort Rosalie.

The Baron de Crenay's Carte de partie de la Louisiane drawn up in Mobile in March 17333 using calculations from relevés à l'estime, provides a relatively accurate portrait of Louisiana's most important travel routes at the time.

In 1731, the Compagnie des Indes retroceded Louisiana to the king. As a result, a large number of manuscripts were passed to royal geographer Jean-Baptiste d’Anville: maps of bays and islands off the coast of the gulf, drawn by captains and pilots of vessels in the service of the Compagnie des Indes; maps of the hinterland, from the Mississippi to the Illinois Country; maps of the Red River, the River of the Alibamons, the River of the Perles and even the Missouri. With these firsthand sources, d’Anville was able to create a map of the colony that better represented the extent of Louisiana and the locations of its water courses, forts and Indigenous villages. He began his Essai d’une carte de la Louisiane in 1732, at a larger scale than anything that had preceded it, using a very great number of French and Indigenous toponyms and drawing curves that indicate the use of surveys made in the field.

 
Knowledge of the Mississippi was essential to the French for several reasons: it shaped decisions on where to build forts or dwellings, helped protect traders bringing furs and flour from the Illinois Country to Louisiana settlements, and allowed French officers to maneuver their troops efficiently during wars with certain First Nations. This is particularly evident in the Carte particuliere d’une partie de la Louisianne, dated 1743, based on surveys carried out by three cartographers in the field. It shows the Mississippi, the Mobile and their tributaries, as well as the dirt paths leading to the land of the Chicachas, a First Nation opposed to French encroachment on their territory.

 

Published in May 2021