In 1673 Louis Jolliet, an experienced woodsman and cartographer, and Father Jacques Marquette, a Jesuit priest, led the first European exploration of the middle Mississippi River region.

Among other remarkable adventures recounted in his journal Father Marquette included the following description of a pictograph, which the expedition observed on the rocky bluffs above present-day Alton, Ill.

"While Skirting some rocks," the priest wrote, "which by Their height and length inspired awe, We saw upon one of them two painted monsters which at first made Us afraid, and upon Which the boldest savages dare not Long rest their eyes. They are as large As a calf; they have Horns on their heads Like those of a deer, a horrible look, red eyes, a beard Like a tiger's, a face somewhat like a man's, a body Covered with scales, and so Long A tail that it winds all around the Body, passing above the head and going back between the legs, ending in a Fish's tail. Green, red, and black are the three Colors composing the Picture. Moreover, these 2 monsters are so well painted that we cannot believe that any savage is their author; for good painters in france would find it difficult to reach that place Conveniently to paint them. Here is approximately The shape of these monsters, As we have faithfully Copied It."

The pictograph was seen subsequently by LaSalle and other French explorers in the 17th century after which the record is silent for a hundred years. Then additional sightings are reported in the early 19th century, and the earliest-known artist's sketch was made in 1825 by William Dennis. He labeled his creation the "Flying Dragon."

In 1836 John Russell of Bluffdale, Ill., published an article entitled "The Bird That Devours Men," and called the monster the Piasa Bird for the first time. Russell related a legend, much of which he created, which persists as the explanation of the pictograph. The Piasa Bird, Russell wrote, was a huge flying monster which lived on the cliffs, destroyed Indian villages, consumed its captives, and resisted efforts to destroy it. Chief Ouatoga, however, during a dream inspired by the Great Spirit, conceived a plan to kill the terrible bird. Using himself as bait and 20 of his bravest warriors to launch poisoned arrows, Ouatoga's plan succeeded and the Piasa Bird fell into the Mississippi and drowned. In commemoration of this event, Russell contended, the grateful Indians placed the image of the Piasa Bird on the bluff.

In 1841 the Piasa Bird was included in a lithograph by John Casper Wild, and in 1846-47 it was sketched by Henry Lewis for a major collection of lithographs which appeared in 1854. Rudolf Friederick Kurz, a visiting Swiss artist, described the pictograph in 1847 as "a colossal eagle," and in the same year John Russell published a revised version of the legend. Speculation continued throughout the 19th century, even after the entire rock upon which the pictograph appeared was quarried away for making lime.

Although there is no way of ascertaining just how the original pictograph looked, the most commonly accepted version was a sketch made by a group of old citizens of Alton which has been reproduced numerous times and is now painted on a cliff along the Great River Road above Alton. Thunder Bird of the Dakota Sioux, medicine animal of the Winnebagos, a figment of Father Marquette's imagination, or avenging monster of the bluffs of the Mississippi River, the Piasa Bird is an indelible part of Illinois legends.