$30.8 million: This 16th-century manuscript by Leonardo da Vinci contains the artist's observations and theories on topics such as astronomy, geology, and hydrodynamics.
$24.5 million: One of only four surviving copies of the Magna Carta, a 13th-century document that established the principle of the rule of law in England.
$14.2 million: The first book printed in what is now the United States, this Puritan hymnal was printed in Massachusetts in 1640.
$14 million: The oldest European book to survive fully intact, this 7th-century Gospel book was discovered in the coffin of St. Cuthbert in 1104.
$6 million to $9 million: The first collected edition of William Shakespeare's plays, published in 1623.
$4.9 million: The first book ever printed using movable type, printed by Johannes Gutenberg in the 15th century.
$4.5 million to $11.5 million: A collection of life-sized illustrations of North American birds by naturalist and painter John James Audubon, printed between 1827 and 1838.
$2.5 million: A collection of poems and illustrations by William Blake, printed in 1794.
$3.98 million: A collection of fairy tales from the Harry Potter universe, handwritten and illustrated by J.K. Rowling.