A man tried to open a display case and steal artefacts from the British Museum on Wednesday.
The museum said security guards apprehended a man
The museum said an attendant spotted the man using a pair of pliers and wire in the Greek and Roman gallery, in central London, near closing time.
In November a security expert said the museum was among several with priceless collections at risk of theft.
Police said a 40-year-old man had been arrested on suspicion of attempted theft and going equipped to steal.
He is being held at Holborn Police Station.
The museum said security guards had apprehended a suspect who they handed over to police.
A collection of about 15 ancient Chinese jewels was snatched from the museum just a few months ago.
A museum spokeswoman said: "A man was spotted by an alert gallery attendant acting suspiciously so they approached him and noticed he seemed to have some wire and pliers in his hand and was seemingly trying to get into one of the cases.
"The gallery contains lots of different objects. There is some jewellery, Roman cameos, glass vessels and some larger sculptures.
"Obviously they are important objects on display in one of our key galleries."
Security Expert Will Geddes, who carried out a covert security review of some of London's top museums last year, said access to the building was extremely easy.
At the time spokesman for the British Museum said it was always looking to improve security.