Police who recovered a stolen Leonardo da Vinci painting have said they never gave up hope of finding the artwork - even after more than four years.
The Madonna with the Yarnwinder was taken from Drumlanrig Castle, in Dumfries and Galloway, in August 2003.
Police officers recovered the £30m painting at a solicitors' office in the centre of Glasgow on Thursday.
Three men from Lancashire and one from Glasgow have appeared at Dumfries Sheriff Court.
Det Supt Brian Anderson said that at the height of the police operation some 60 officers were involved in searching premises in Glasgow and Lancashire.
Police said up to 60 officers were involved in the operation
"Dumfries and Galloway Constabulary has constantly had officers dedicated to this inquiry and never gave up hope of recovering the painting," he said.
The painting was discovered during a raid at the offices of HBJ Gateley Wareing in West Regent Street, Glasgow.
It's understood that a lawyer was among those arrested.
Deputy Chief Constable George Graham said the masterpiece was now in safe storage in a vault at an unspecified location.
He added that the investigation was ongoing and that there were a number of leads still to be followed up.
Thanking all those involved in tracking down the painting, he added: "This has been a particularly challenging and long-running inquiry and we could not have brought it to this particular stage without the help of these agencies."
The artwork depicts the Madonna with the infant Jesus holding a cross-shaped yarnwinder.