Among the ornate rooms and historic artworks at the Royal Palace of Madrid is a surprise for anyone who wants to catch a glimpse of music history.

Known as the Royal Quartet, the foursome of stringed instruments kept at the palace are unique examples of the work of Antonio Stradivarius, the renowned Italian instrument maker. The Royal Palace’s quartet—two violins, a cello, and a viola—are among the eleven decorated Stradivaris in known existence. 

The ivory-inlaid quartet were offered as gifts to King Felipe V in 1702 by Stradivarius, and are the only set of decorated instruments the master is known to have made. The quartet was originally a quintet and contained another viola. Both violas were stolen by French troops during the Napoleonic wars; one was recovered in the 1950s, but the other remains missing today. 

For most Palace visitors, the quartet is a look-but-don’t-touch experience. One group is an exception, though. The Royal Palace hosts public concerts featuring their quartet-in-residence, Cuarteto Quiroga, where visitors can see and hear these rare instruments in action.

“They were created in order to make music,” explained music adviser Álvaro Guibert to The Strad magazine, “so not playing them would be denying them their fulfillment.” Since being reunited with the stolen viola, the quartet has never left the Royal Palace, and according to Guibert never will again.