A burglary that took place at the Château de Fontainebleau early Sunday morning has left French investigators searching for 15 gold and bronze artworks, including a bejeweled crown that once belonged to the king of Siam.

The New York Times reports that the robbers broke into the castle shortly after six A.M. and were out within at least seven minutes, the time between when the alarm sounded and police arrived on the scene. Officials have determined the theft was the work of “professionals.”

The missing treasures, all from the 18th century, were taken from the Chinese wing of the castle. Most were part of the collection of precious artifacts amassed by Empress Eugenie, wife of Napoleon III.

The crown, which was made of solid gold punctuated by precious stones and pearls, is thought to have been the main motivation behind the burglary. It was given to Napoleon III in 1861 as a gift from the ambassador of Siam. Also taken was a Tibetan mandala from the same period.

An estimate of the value of the works taken has not been provided, as they are all considered priceless. The last time there was a robbery at the Fontainebleau was in 1995. Strangely the exact same number of artifacts was taken in that burglary, nine of which were eventually recovered.

The crime is currently being investigated by the Fight Against Trafficking of Cultural Goods, a special French unit that tracks stolen works of art and cultural objects. Here’s to hoping this doesn’t join the ever-growing list of Unsolved Art Heists.