Two men have been arrested on suspicion of burglary after Bronze Age gold jewellery was stolen from St Fagans National Museum of History in Cardiff.
The men, aged 43 and 50, from Northampton were arrested on Tuesday afternoon and are in custody in Northamptonshire.
Police were called to the museum on the outskirts of the city at about 00:30 BST on Monday and several items, including Bronze Age jewellery, were stolen from a display case in the main building.
South Wales Police said it was still searching for the stolen items.
Police said a helicopter was at the scene five minutes after being called by onsite security staff.
Det Insp Bob Chambers thanked the museum, Northamptonshire Police, and the public for their “continued support”.
Museum Wales said it was “pleased to hear of this significant development in the investigation”.
The museum added it was “hugely grateful” to police and would continue to work with them.
Founded in 1948, St Fagans is one of Wales’ most popular heritage attractions and is one of seven national museums under the curation of Amgueddfa Cymru, which is Welsh for Museum Wales.
The authorities have so far not specified which items were taken, or their value. The museum’s Bronze Age collection includes gold ingots, bracelets, and a lunula necklace.
According to Museum Wales, the Bronze Age, which took place between about 2300BC and 800 BC, saw jewellery used to display wealth and status.
Earlier on Tuesday, Jane Richardson, chief executive of National Museum Wales, described footage of the break-in as “emotional to watch”.
She said: “It’s been very upsetting for us all. We’re absolutely devastated.
“These items don’t belong to us at the museum, they belong to the people of Wales.
“The Amgueddfa is a family which everyone in Wales belongs to, and it feels like the family of Wales has been attacked,” Ms Richardson added.
Welsh politicians have raised concerns about the safety of museum collections in the Senedd earlier.
Heledd Fychan, Plaid Cymru MS for South Wales Central, called for assurances that collections across Wales were safe.
Jane Hutt, Wales’ social justice secretary, condemned the “horrific loss” and confirmed that security had been strengthened across all Museum Wales sites.
