London's Whitehall was brought to a standstill for nearly three hours as a naked man straddled a statue in front of hordes of onlookers.
He was seen in a variety of poses on the statue of Prince George, the Duke of Cambridge, at times balancing precariously on the duke's head.
The man was coaxed down shortly before 3pm on Friday (0200 AEDT on Saturday) and detained under the Mental Health Act, police said.
Officers were called around midday to reports that someone had clambered on to the statue, and might have a knife.
A 100-metre stretch of Whitehall, near the heart of Westminster in central London, was cordoned off as emergency services tried to persuade him to come down.
The man was seen waving his arms around and was talking to crews on the ground as crowds of onlookers gathered at either end of the cordon.
Whitehall runs from Trafalgar Square and is where the Ministry of Defence is situated.