They called it 'Operation Pandora', a joined operation by police authorities from 18 European Union member states, UNESCO, the World Customs Organization, Europol and Interpol aimed at dismantling an international network of art traffickers. And it succeeded.

Operation Pandora began in October and ended in December. Its aim was to crack down on trafficking in Europe of antiquities from the Syria and Iraq war zones, as well as works stolen from museums and other sites.

In the southern Spanish city of Murcia, the police recovered about 500 archaeological pieces, including 19 stolen from the city’s archaeological museum in 2014. In Greece, the authorities recovered part of an Ottoman tombstone, Byzantine objects and an image of St. George dating to the 18th century. The Spanish police also released a photograph of ancient coins, some of which were recovered by tracing online sales. The Spanish authorities, however, did not provide a detailed inventory of the recovered objects, and would not confirm where the arrests were made.

A spokesman for Spain’s Interior Ministry said the investigation was disclosed this weekend only after it was completed, even though the arrests occurred earlier. According to Europol data, 3,561 ancient objects were confiscated and 75 people were arrested. A total of 29,340 vehicles and 50 ships were searched. Over 500 objects were found in Murcia, Spain, stolen from the city museum. Altogether, the statement said, more than 48,000 people were investigated. Lauren Frayer reported for NPR from Madrid:

"Spanish police say the suspects are members of criminal gang that trafficked stolen art and archaeological relics. They have been under investigation for months, by law enforcement from 18 countries, led by Spain and Cyprus. Altogether, police say they have recovered about 3,500 pieces of stolen art — including Byzantine relics and an Ottoman tombstone in Greece. Among those found in Spain were 19 artifacts stolen from an archaeology museum three years ago. Police have not issued a complete inventory, but said most of the artifacts were taken from countries at war."

UNESCO said authorities in Austria, Belgium, Bulgaria, Bosnia- Herzegovina, Cyprus, Croatia, Germany, Greece, Italy, Malta, Netherlands, Poland, Portugal, Romania, Serbia, Spain, Switzerland and the U.K. all participated in the investigation.