Founded in the 16C by Augustus the Young, and rebuilt at the end of the 19C, this was the largest and most important library in 17C Europe. Still an invaluable treasure house for researchers and scholars, it houses some 600 000 volumes. Among the priceless documents and illuminated manuscripts from the Middle Ages is the 12C Helmarshausen Gospel, said to have belonged to Henry the Lion. Globes, maps and a portolan provide interesting information on the state of geographic knowledge in the 15C, 16C and 17C.