The Library of Congress, the oldest federal institution in the United States (founded in 1800), was destroyed by the British in 1814. The collection was reestablished with the purchase of Thomas Jefferson's private library in January 1815. According to the LOC, "Jefferson's collection contained 6,487 volumes in the fields of politics, history, science, law, literature, fine arts, and philosophy and was recognized as one of the finest private libraries in the United States."
At the time of the purchase, some members of Congress objected that the collection "was too philosophical, had too many books in foreign languages, was too costly, and was too large for the wants of Congress." Contra these opponents of the acquisition, others referred to Jefferson's proposition that "There is, in fact, no subject to which a member of Congress may not have occasion to refer."
This probably sounded rich coming from Jefferson. His interests included architecture, archeology, natural and speculative philosophy, religion, and of course Politics. His private library reflected this diversity. And as the years have passed, the weight of Jefferson's character have added to the historical importance of the collection. For example, Jefferson's copy of the Qur'an was used in the swearing in of Rep. Keith Ellison, the first muslim elected to Congress. (Washington Post 1/3/07)
On the basis of these considerations, I nominate Jefferson's library as a candidate for the Greatest Private Library in history.
