Tower Rock, a small limestone island in the Mississippi River, long stood as a striking landmark for travelers and navigators. Jacques Marquette noted it in 1673, and when Lewis and Clark passed through the area 200 years ago, Meriwether Lewis found it so commanding that he wrote about it at length in his journal after climbing a nearby summit and taking in the bold hills and surrounding countryside. The island was more than an impressive natural feature: to navigators it was legendary, because when the river flooded a dangerous whirlpool formed as the violent current of the second channel forced its way between the rock and the base of a nearby formation. For Mississippi boatmen, passing it for the first time became a rite of passage, marked by grand celebration or dunking in the river. Only 23 days into their journey, Lewis and Clark were already encountering the beautiful landscapes that lay ahead.