A woman was attacked and raped while walking on Hob Moor in York.
It happened at around 4am to 4.30am on Sunday (May 30).
Police have stepped up their patrols on the ancient common.
A North Yorkshire Police spokesperson said: “We’re appealing for information as part of a rape investigation in York.
“It happened on Hob Moor at around 4am to 4.30am on Sunday.
“A number of lines of enquiry have been carried out which lead us to believe this was an isolated incident.
“A young woman was walking across Hob Moor in a south-eastern direct from the west when she was approached by a man and assaulted.
“The man is described as a slim build and wearing black trousers, a black hooded jacket and black gloves.
“A full investigation is currently underway, and there has been an increased police presence in the area.”
Anyone with information about the incident, or who saw anyone acting suspiciously, is urged to contact North Yorkshire Police on 101 and select option 1, quoting reference 12210128446.