WASHINGTON, D.C. (WHTM) — It’s been called the nation’s attic. The Smithsonian Institution, established this day in 1846 by an act of Congress, has grown into the world’s largest museum complex with 19 buildings in two cities, Washington and New York.

And it all started with a bequest by a British citizen who never visited the United States.

James Smithson (c. 1765-June 27, 1829), was a chemist and mineralogist, member of numerous scientific organizations, son of Hugh Smithson, Duke of Northumberland, and author of a most unusual will. When he died in 1829, he left his fortune to his nephew, with a stipulation that if his nephew died without heirs, his estate would go to the United States “to found at Washington, under the name of the Smithsonian Institution, an establishment for the increase and diffusion of knowledge among men.”

His nephew, Henry James Hungerford, died childless in 1835. Suddenly the U.S. Government had a big chunk of money on its hands — an estate valued at $500,000, or about $15,928,817.20 in today’s money. Congress accepted the donation in 1836, then spent the next eight years hashing out what to do with it. Should it be a research lab, a library, a university, an astronomical observatory, or a museum?

The Smithsonian is mostly a museum — or museums — but it’s also a little of everything else. Starting with The Castle, the first Smithsonian Building on the National Mall in Washington, it’s grown into:

Smithsonian Institution Building (The Castle)

Arts and Industries Building

National Air and Space Museum

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National Air and Space Museum Steven F. Udvar-Hazy Center

Smithsonian American Art Museum

National Museum of American History

National Museum of the American Indian

National Museum of the American Indian George Gustav Heye Center (New York City)

Anacostia Community Museum

Arts and Industries Building

Cooper Hewitt, Smithsonian Design Museum (New York City)

Freer Gallery of Art

Hirshhorn Museum and Sculpture Garden

National Zoo

National Museum of Natural History

National Portrait Gallery

National Postal Museum

Renwick Gallery of the Smithsonian American Art Museum

Arthur M. Sackler Gallery

Smithsonian Gardens

In 1903, Smithson’s remains were brought to the United States and reinterred in the Castle. To this day, nobody knows why Smithson made the bequest that started his amazing institution.