At 4:59 a.m. on Monday, police were notified that a break-in was underway at Dresden Castle in the eastern German state of Saxony. CNN reports that the thieves stole more than 100 items from the Green Vault, one of Europe’s largest collections of jewels, ornaments, and other priceless treasures.

According to the BBC, the thieves entered by partially detaching an iron grille from a window on the ground floor, and proceeded to steal three of the museum’s 10 diamond sets, which also include rubies, emeralds, and sapphires.

Augustus the Strong, who ruled Saxony in the early 18th century, founded the Green Room as Europe’s first public museum, filling it with valuables as a way to promote Dresden as a center for the arts. According to CNN, the rooms feature “shimmering bowls carved out of crystal and agate to jeweled gold figurines to the Dresden Green, the largest and finest green diamond in the world.”

Though police and museum personnel are still trying to confirm the full extent of the heist, the director of Dresden’s State Art Collections, Marion Ackermann, said the historical significance of the pieces makes their value difficult to calculate. One, for example, is a 648-carat sapphire that Russian tsar Peter the Great gave to Saxony as a gift.

She said the jewels’ fame will prevent the criminals from selling any pieces legally, but the thieves may try to dismantle the sets and sell them piece by piece on the black market.

Saxony’s prime minister Michael Kretschmer took to Twitter to express his outrage at the heist, saying that it wasn’t just the museum that had been robbed, but the people of Saxony, too.

To track down the thieves, police are working off CCTV footage that shows two suspects on the premises, as well as the burned remains of a car—possibly a getaway car—found in the city early Monday morning.

[h/t CNN]