Wiltshire Police is appealing for witnesses who might have been in the vicinity of Handel Street, Poulton Street or Ferndale Road between midnight and 3am on Sunday.
The victim, a 28-year-old woman, was walking home after a night out in the Cricklade Road area of Swindon shortly after midnight on Saturday.
The first incident took place in an alleyway between Handel Street and Poulton Street.
The victim was subjected to a serious sexual assault by a male described as black, with short shaved hair and of medium height.
After the attack, the victim continued on her walk home when she was subjected to a second sexual attack by another male.
This second incident took place in the alleyway which separates Ferndale newsagents with Fitz-patrick’s Boxing Gym in Ferndale Road. The suspect is described as being black, of a stocky build with a muscular frame.
After the incident, the victim managed to flee the scene and get back to her home address.
Police received a call after the second incident and not in the time between the attacks.
The victim told police that during the second attack she managed to scream.
Both incidents took place sometime between 00.01am and 2.50am on Sunday morning.
Two men aged 34 and 37, both from Swindon, have been arrested on suspicion of rape. The 34-year-old has been released on police bail pending further enquiries and the 37-year-old remains in police custody at the time of going to press.
Detective Sergeant Phil Walker, from Swindon CID, said: “Firstly, I would like to commend the victim in this case for contacting Wiltshire Police immediately after getting home – this allowed us to gather crucial evidence.
“Wiltshire Police are robustly investigating both incidents and are keen to hear from anyone who may have seen or heard anything suspicious between midnight on Saturday and 2.50am on Sunday in the Ferndale Road, Handel Street and Poulton Street areas of Swindon.”
Anyone with information is asked to contact Wiltshire Police on 101 or Crimestopp-ers on 0800 555 111.
A police car and crime scene investigation van were parked outside the gym in Ferndale Road, which is owned and run by boxing trainer Paddy Fitzpatrick, from the early hours until 10.45am on Sunday.
The alleyway was cordoned off with police tape. Employees at the neighbouring newsagents said the police had been on the scene before they opened at 5am.