Posted Sunday, June 30, 2002; 8:31 a.m. EST
They spent roughly a thousand days and nights together, from the rainy October morning they left the falls of the Ohio until they finally pulled their canoes out of the Mississippi three years later in St. Louis. They slept in impossibly close quarters, often sharing the same buffalo-skin teepee with an Indian woman, a French-Canadian interpreter and their baby. They, and several enlisted men, kept journals whose published throw weight equals 13 volumes, 30 lbs., 18 in. of bookshelf and approximately 1 million words. All that evidence notwithstanding, the more we learn about the two captains who gave their names to the Lewis and Clark Expedition, the more powerful becomes their pull on our imagination.

Historians traditionally distinguish them by contrasting their personalities — the brooding Meriwether Lewis played off against the genial William Clark — Jeremy Irons hitting the road with John Goodman. Gary Moulton, editor of the explorers' journals, says, "The differences existed, but they may have been exaggerated." In reality, the two men had far more in common. They were both Virginians. They were both Army officers, six-footers and experienced outdoorsmen, who first met eight years before the expedition when they were serving in Indian campaigns in the Ohio Valley. They shared with their friend Thomas Jefferson a passion for such Enlightenment sciences as ethnology, paleontology, zoology and botany.

They were both fearless spellers. Clark took "Looner" observations, ate slices of "Water millions," tracked "bearfooted Indians" and was proud to serve the "Untied States." Clark's spelling is more famously imaginative — he found 27 different ways to spell the word Sioux. (In fairness, even the best-educated Americans displayed erratic spelling until Noah Webster's dictionary standardized spelling two decades later.)

Older than Lewis by four years — they were 33 and 29 when the expedition began — Clark was the more experienced soldier and frontiersman. His five older brothers had fought in the American Revolution. One, General George Rogers Clark, had led raids that kept the lower Great Lakes region out of British hands. As an Army officer, William had trekked the Ohio Valley, leading troops at least once in a skirmish with Indians. "He is a youth of solid and promising parts, and as brave as Caesar," reported a family member.

But by 1803 George was sinking into alcoholism, and William had resigned his commission in part to help settle his brother's debts. The two were living together on a point of land overlooking the Ohio River just below Louisville when William received an astonishing letter from his old Army buddy.

For the previous two years, Lewis had been working in the White House as Jefferson's private secretary. Like Jefferson, Lewis had lost his father at an early age; now he was in daily contact with the President, who was practically a surrogate father to him. Lewis told Clark that Jefferson had placed him in charge of a mission to explore "the interior of the continent of North America, or that part of it bordering on the Missourie & Columbia Rivers." Moreover, Lewis wanted Clark to be his co-commander.

Jefferson had once discussed a similar mission with George Rogers Clark. But now, leaving George in his family's care, William accepted "chearfully," and "with much pleasure" — just in time to prevent Lewis from signing up his backup choice, an Army lieutenant named Moses Hooke.

Lewis and Clark got along well from the start. When Clark's anticipated commission as a captain instead came through as second lieutenant — a misstep that still rankled years later — they never told their men and treated each other as equals — placing them among the few effective co-ceos in organizational history.

They apportioned their operating responsibilities: Clark was the better boatman and navigator, Lewis the planner and natural historian, often walking ashore far ahead of the vessels being laboriously hauled against the Missouri's current. Clark clearly had the cooler head. He brokered the crucial early compromise that ended a staredown with the Teton Sioux. The more mercurial Lewis hurled a puppy into the face of an Indian who angered him, and killed a Blackfeet in the corps's only violent incident.

During their long winter at Fort Mandan, near today's Bismarck, N.D., Lewis and Clark encountered Charles McKenzie, a British trader who later wrote,"[Captain Lewis] could not make himself agreeable to us. He could speak fluently and learnedly on all subjects, but his inveterate disposition against the British stained, at least in our eyes, all his eloquence. [Clark] was equally well informed, but his conversation was always pleasant, for he seemed to dislike giving offense unnecessarily."