Dutch treasure hunter Lorenzo Ruijter had been unsuccessfully scanning the ground for nearly three hours when his metal detector finally went off. He started digging and, to his surprise, unearthed 39 silver coins, 2 strips of gold leaf and 4 gold earrings.

Ruijter made this startling find in 2021 near Hoogwoud, a small city north of Amsterdam. But for the past two years, he’s had to keep his treasure a secret while experts at the Dutch National Museum of Antiquities studied and dated the artifacts.

Now, the museum has revealed that Ruijter’s treasure is likely 1,000 years old. Based on the dates of the newest coins, the museum’s experts say someone buried the treasure around 1200 to 1250 C.E. At that time, the pieces of jewelry were already 200 years old, which suggests they were someone’s “expensive and cherished possession,” says the museum in a statement, per Google Translate.

“It was very special discovering something this valuable; I can’t really describe it,” says 27-year-old Reuijter to Reuters’ Charlotte Campenhout. “I never expected to discover anything like this.”

After cleaning the medieval items, researchers were able to learn more about them. The four earrings, for example, date to the 11th century, per the museum. They’re shaped like crescent moons and are about two inches (five centimeters) wide. One pair features an engraving of the head of Jesus Christ surrounded by rays of sun, while another is decorated with thin, twisted threads made from gold balls, a type of decoration known as filigree. Since the earrings have delicate suspension brackets and are only decorated on one side, they were likely worn on a headband or a hood, rather than in pierced ears.

“Comparable gold earrings have only been found three times in the Netherlands,” says the museum in the statement.

Researchers found small textile fibers attached to the two strips of gold leaf, which suggests they were likely worn on the waistband or edge of a piece of clothing.

They also found small pieces of textile among the 39 silver coins, which suggest they were at one time wrapped up in a bag or piece of cloth. The coins include tokens from the Roman Catholic Diocese of Utrecht, as well as pennies from several counties in the Netherlands and from the German Empire. Some of them were made in 1247 or 1248 under the rule of William II.

While historians know the treasure’s age, they still have a lot of unanswered questions. They don’t know, for instance, who buried the artifacts—or, perhaps more importantly, why.

One theory, experts say, is that someone wanted to keep their most prized possessions safe during a mid-13th century war between the Dutch regions of West Friesland and Holland. The treasure’s owner may have been a noblewoman fleeing the war, according to the London Times’ Bruno Waterfield.

The treasure’s burial during this period of fighting makes the find “of great significance for the archaeology and history of North Holland and West Friesland—and even of national and international importance,” per the museum’s statement.

Eventually, Ruijter will get to keep the treasure. But for now, he’s loaning it to the museum, where it will be on display until mid-June. Beginning in mid-October, it will become part of the museum’s temporary “The Year 1000” exhibition.