Of the province of Louisiana no general map, sufficiently correct to be depended upon, has been published, nor has any been yet procured from a private source . . . surveys have never been made on so extensive a scale." Thus the first sentence from the set of documents submitted by President Thomas Jefferson to Congress justifying the American purchase of the Louisiana Territory.
When Robert Livingston and James Monroe asked Napoleon what it was precisely that they had purchased, he responded that the territory was that which had been retroceded by Spain to France. When Napoleon's foreign minister, Talleyrand, was further pressed to be explicit, he repeated that formula, and added that he hoped the United States would "make the most if it."
President Jefferson was energetic in his determination to maximize the boundaries of that new territory. He and Livingston were absolutely certain that the Gulf Coast was ours—what then was known as the Floridas. They hoped that the territory might include a chunk of what is now Texas, but that was hardly certain. Jefferson did send exploring expeditions into the Red River country of what is now the state of Louisiana, and would send Lt. Zebulon Pike up to the Lake of the Woods in Minnesota to see if that boundary might be pushed farther north. But the greatest stretching would take place in the far west—with Lewis and Clark searching for the Northwest Passage that would lead to the Orient.
The United States had to buy the Floridas—and did so following the 1812 war. Spain's claim to the coastline along the Gulf of Mexico was clear—no matter what Napoleon had said. The country would have to settle, eventually, on the forty-ninth parallel as the northern boundary. Yet what wonderful things might be found in that great northwest?
Lewis and Clark felt an immense responsibility to record their observations so minutely, so clearly, that any claim based upon their work could be sustained. It would be wrong to see the venture—the adventure—as a business trip. There was an important and psychologically sustaining romance about it. They would be the first American adventurers to view these new vistas. As Lewis explained to each tribe they encountered, we are on a "long journey to the Great Lake of the West, where the land ends."
Limits to the Louisiana Territory were defined by watersheds. That was a well established European custom. Determining the extent of the upper Missouri watershed was the single most important task they faced. The result was that they spent more time in what is now Montana than in any other area. Their search for the westernmost source of the Jefferson River nearly cost them their lives. They traversed the Bitterroot mountain range so late in the season that winter almost trapped them in a death cycle of fatigue, starvation and despair.
On the return leg of the journey, Lewis chose to explore the Marias River in an effort to establish the northern boundary of the Missouri, hoping it would prove to be above the 50th parallel.
The weight of responsibility upon the captains was doubly heavy because now their country owned the Louisiana country—and, like good Americans, they were going to make the most of it.
William Clark's remarkable mapmaking skills were coupled with Lewis's power of observation to produce a cornucopia of valuable information about an extremely valuable area. Yet even those gifted explorers could not encompass the precise measurements necessary to define the territory. Indeed, that was not accomplished until the second decade of the twentieth century. The area west of the Mississippi is now to be 828,000 square miles. General Horatio Gates, writing to President Jefferson, July 18, 1803, expressed a common feeling when he said: "Let the Land rejoice, for you have bought Louisiana for a song."