A man has been seriously injured in an assault outside the National Museum of Scotland in Edinburgh.
The 21-year-old man suffered a head injury during the attack, which took place around 2am on Sunday at the junction of George IV Bridge and Chambers Street.
He was taken to Edinburgh Royal Infirmary after the attack.
Police are trying to trace a group of four men who were seen walking north on the bridge and believe a passer-by may have mobile phone footage of the incident.
Detective constable Iain Wallace, of Gayfield CID, said: "We're currently working to establish the full circumstances surrounding this assault and are eager to trace anyone who may have witnessed this.
"We believe that a passer-by may have video footage or images of the attack on his mobile phone and would urge this person to get in touch with us as soon as possible to help with our enquiries."
Anyone with information can contact Police Scotland on 101, quoting incident number 0607 of December 3.