The plots to raid British museums of Chinese artefacts dwarfed the more high profile Hatton Garden safety deposit box break-in, a senior detective said.
Putting an exact figure on the items the gang managed to spirit away from Cambridge's Fitzwilliam Museum and almost got away with taking from the Oriental Museum in Durham was tricky, but it was estimated at £18-£57 million.
The Hatton Garden raid was thought to have been worth £14m.
Detective Superintendent Adrian Green, of Durham Police, said of the museum thefts: "If you think the Hatton Gardens break-in was big, this will blow that out of the water."
Mr Green was first involved when raiders broke in to the Oriental Museum at Durham University in April 2012.
Commercial burglars broke through walls the night before Good Friday, burst in and swiftly grabbed an exquisite jade bowl and a figurine, then fled.
The detective said: "The bowl is Ming Dynasty and is one of the best in the world with a value of in excess of £2m and as high as £16m."
The items were found by police on waste ground a few miles from the museum, but the gang went looking for other jade bowls, having missed out on the Durham one.
Another team of burglars, one aged just 15, was instructed to strike at the Fitzwilliam Museum, cutting through shutters and getting away with 18 items. None have been recovered.
Their value has been estimated to be between £16m and £40m. Police linked the two raids and asked other forces around the country for examples of crimes involving auction houses and museums, Chinese artefacts or rhino horn and elephant tusks.
The National Crime Agency took on the role, with support from the CPS, HMRC, Europol and the Covert Asset Bureau in Dublin.
It came to light that a rhino horn libation cup worth £250,000 had previously been taken from Durham Oriental Museum.
And a team of criminals had gone to Norwich Castle Museum and tried to steal a heavy rhino head that was on display, but they were tackled by members of the public and had to dump the cumbersome trophy.
There was an attempted theft from an auction house in Lewes, East Sussex, in March 2013 where criminals posing as customers leapt over the counter and grabbed a £20,000 bamboo cup instead of a libation cup worth 10 times that amount.
The Kelvingrove Museum and the Burrell Collection in Glasgow were also targeted in March 2012 for Chinese artefacts, but the gang failed to steal anything.
A countrywide team of 24 detectives looked for the international figures who instructed individual teams of thieves and pieced together a huge investigation.
It led to 25 people being arrested in England and Northern Ireland, with 40 premises searched including properties in the Republic of Ireland and Spain.
Mr Green said the gang leaders were cowards.
"If you look at the audacity of what they do and the value of the property that they have taken, I think that makes them significant criminals both within the UK and potentially across the world," he said.
"I also think they are cowards because they hire in others, some of them vulnerable, some of the children, to actually do the dirty work.
"They do that while they are at safe distances, sometimes in another country, so they cannot be caught... But they can."
Museum security has been beefed up as a result of the case.
Mr Green said: "They are a bit like banks where people can come in and touch the money.
"Their job is to hold items for the public and let them see them and it is quite difficult for them to get the balance right.
"The higher the security, the higher the budget to maintain that security.
"The difficult thing is, it is all driven by China's economic boom."