During the Middle Ages the authenticity of important documents was established through the use of a seal. These seals were images carved into a matrix which, when pressed into a soft substance, left behind an inverse of the picture on the seal. This remarkable collection of medieval seals comes from the Medieval Institute at the University of Notre Dame, and the online exhibit was constructed by a team of researchers, including Dr. Marina Smyth and Ren'e R. Trilling. The seals found here are facsimiles, and visitors can browse them by categories that include municipal seals, guild seals, and university seals. Most of them are of French origin, though visitors shouldn't miss the amazing Secret Seal of the city of Lund in Sweden or the grandeur that is the Great Seal of the University of Heidelberg from 1386. Finally, visitors can browse around the seals by century or country of origin.