Philosophical Hall is the only privately owned building on Independence Square, as property of the American Philosophical Society. Founded in 1743 by Benjamin Franklin to “promote useful knowledge,” it is the oldest learned society in the country. The word “philosophy” once had a much broader context, and the society was intended to encourage thinking about all sorts of topics, including science, nature, machinery, industry, and government.

Its esteemed list of past and present members includes Benjamin Franklin, Charles Darwin, Madame Curie, Albert Einstein, Toni Morrison, Nelson Mandela, more than a dozen U.S. presidents, and 200 Nobel Prize winners.

The federal-style building was constructed 1786–1789 by Samuel Vaughan and remodeled in 1949 by Sydney Martin. It contains one of the nation’s first museums, founded in 1784 by Charles Wilson Peale, artist, naturalist, and Society member. The museum closed in the early 19th century and did not reopen until 2001. Today, it features rotating exhibits of art, science, and early U.S. history.

Library Hall across the street is also owned by the American Philosophical Society and houses many of its most important collections, including original journals of Lewis and Clark, a copy of the Declaration of Independence in Jefferson’s handwriting, and first editions of Sir Isaac Newton’s Principia and Charles Darwin’s Origin of Species.

The original Library Hall was built in 1790 by architect William Thornton. It was home to the Library Company of Philadelphia, the first public library in the country, founded by Benjamin Franklin, and served as Library of Congress when Philadelphia was the capital. When the Library Company outgrew the space, it relocated to a larger location at 1314 Locust Street, where it operates today.