At an eye-glazing 1,117 pages and a wrist-snapping 15 pounds, the newly published "Renaissance Medals" is the most imposing contribution yet to the National Gallery's systematic catalogues of its holdings. A team of scholars dedicated more than two decades to documenting all 957 of the volume's medals, representing the most important such collection in America. That would have seemed perfectly appropriate to the lords who commissioned these medals and to the artists who made them. We may relegate such objects to neglected galleries and storage rooms (the National Gallery has a few cases of medals on view, but the bulk of the medals languish in drawers), but they were once considered absolutely brilliant works of art. After all, what lord or lady would prefer a single painted portrait, when an image cast in bronze or gold, and then recast dozens of times, could spread a likeness far and wide and preserve it for the future? One of the most famous, best-documented of Renaissance medals was cast in 1498 for Isabella d'Este, Marchesa of Mantua, a great patron of the arts. (Mantegna, Leonardo and Titian all worked for her.) In 1507, Jacopo d'Atri, her representative at the royal court of Aragon in Naples, wrote her about the splash that medal made when its maker, the artist Giancristoforo Romano, appeared with his creation.