Thieves stole most of the Treasure of Villena, a major Bronze Age collection, from a museum in Villena, Spain, early Thursday. The alarm sounded at 5:20 a.m., and the intruders left the building four minutes later, at 5:24 a.m. Authorities said the group likely entered through a window after arriving near the museum in several vehicles.

The collection contains more than 50 objects, including 29 bracelets, 11 bowls and three bottles. Mostly made of gold, it also includes silver, iron and amber artifacts dating to about 1000 BC. Archaeologist Jose Maria Soler discovered the treasure in 1963 in a buried vessel beneath a dried-up riverbed in Villena. The mayor estimated the gold alone at about $2 million, while its historical value was described as nearly impossible to determine.

Mayor Fulgencio Cerdan said the thieves took “most of the collection” and called the loss devastating for Villena’s heritage. Officials said all security systems activated and denied a museum security failure. Investigators are examining whether an earlier alarm at a city sports center was intended to distract security staff. The theft has renewed debate over museum security across Europe.