This section is from the book "The National Capitol. Its Architecture Art And History", by George C. Hazelton, Jr. Also available from Amazon: The National Capitol Its Architecture Art and History.
The Discovery of the Mississippi was painted by William H. Powell. Some of the drawings for it were made in Paris, and it shows unmistakably the influence of French art. It has, perhaps, as little claim to historical merit as any picture ever painted, and is as purely fanciful in color as in the handling of the theme. The bright armor, gay trappings and prancing horses do not befit that ill-starred expedition which, starting from Spain in 1538 six hundred strong, arrived on the coast of Mexico in 1543 an enfeebled remnant of less than half that number, glad to have escaped with life the inhospitable swamps and savages. De Soto, in search of the realization of his golden dreams, found only a grave beneath the waters of the mighty Western river.
The picture, however, is remarkably pleasing for its vitality, admirable dramatic grouping and buoyancy of effect. It was painted in accordance with an act of Congress of 1847, authorizing the Library Committee to contract for an historical picture to take the place of the one which Henry Inman, an original contractor, had left unfinished at his untimely death. As Inman had already received three instalments of $2,000 each, there were but $4,000 still available on the unexecuted contract; $6,000 besides were directly appropriated to Powell for the present painting. On March 3, 1855, Powell received an additional appropriation of $2,000, making the total cost to the government for the adornment of the panel $12,000.