Four men have been arrested over alleged slavery offences spanning a period of 26 years.
They were held today by detectives investigating alleged offences against two men including slavery, servitude and kidnap.
An operation involving three police forces saw warrants executed at five addresses in Bristol and Cardiff this morning.
Four men from the Rumney area of the Welsh capital were arrested, Gwent police said.
Three - aged 57, 37 and 33 - were held on suspicion of knowingly or conspiring to hold a person in slavery, servitude or requiring another person to perform forced or compulsory labour, kidnap, false imprisonment and assault.
A fourth man, aged 34, was arrested on suspicion of knowingly or conspiring to hold a person in slavery, servitude or requiring another person to perform forced or compulsory labour and assault.
A Gwent Police spokeswoman said all four arrests relate to two victims, adding: "We are investigating allegations covering a period of 26 years."
Detectives are investigating allegations of slavery, servitude and forced labour in relation to one of the men, while claims of kidnap, false imprisonment and assault are being probed in connection with the second alleged victim.
Police are not disclosing the ages of the women, only confirming that they are adults.
The spokeswoman added that both are "safe and being supported by police".
The arrests were made by officers working on Gwent Police's Operation Imperial. South Wales Police and Avon and Somerset Police were also involved in today's operation.
Lead officer Detective Superintendent Paul Griffiths said: "The alleged offences we are investigating are extremely serious and we would urge anyone with any information which could assist to contact the Imperial team directly by dialling 01633 647174.
"Alternatively if someone has information and would rather not pass this directly to the police then I would urge them to contact Crimestoppers, which is independent of the police and guarantees complete anonymity on 0800 555 111."