A 44-year-old was raped in a lane in Edinburgh’s Fleshmarket Close.
Police Scotland said they believed the attack took place at about 03:00 just off the High Street.
A man had been detained by police in connection with the incident.
A Police Scotland spokesman said: “Police in Edinburgh are investigating following a report of serious sexual assault on a 44-year-old woman.
“The incident happened sometime around 3am on Wednesday, December 6, in the High Street area.
“A man is currently detained in connection with this inquiry, however, anyone who believes they may have information relevant to the ongoing investigation is asked to contact police immediately.”