Six prisons in England are being closed as work begins on plans to create Britain's biggest jail in a move to drive down costs.
Some 2,600 offenders are held at the prisons targeted for closure. Another three sites will be partially shut down.
The prisons shutting are Bullwood Hall in Essex, Canterbury, Gloucester, Kingston in Portsmouth, Shepton Mallet in Somerset and Shrewsbury.
Facilities in Chelmsford, Hull and the Isle of Wight will also see some accommodation reduced.
The new "super prison" will be built in either London, the north west or north Wales and could hold more than 2,000 criminals.
A feasibility study on the project is now set to start, the Ministry of Justice (MoJ) announced.
The programme is part of a move to replace older jails and cut prison costs. The Government claims it will save £63m-a-year.
Justice Secretary Chris Grayling said: "We have to bring down the cost of our prison system, much of which is old and expensive.
"But I never want the courts to be in a position where they cannot send a criminal to prison because there is no place available.
"So we have to move as fast as we can to replace the older parts of our prison system."
Mr Grayling's stance contrasts with his predecessor Ken Clarke, who wanted more community sentences to ease the pressure on the prison system.
As well as the super-prison, there are plans for four new mini-prisons known as houseblocks which could hold up to 1,260 prisoners.
These are due to be built at existing prisons in Parc in South Wales, Peterborough in Cambridgeshire, the Mount in Hertfordshire, and Thameside in London.
The young offenders institution at HMP Ashfield is being converted into a full adult prison and some 200 contractually crowded places are private prisons will be decommissioned.
The announcements follow the opening of the new G4S-run HMP Oakwood near Wolverhampton last year, which has a normal capacity of 1,600 prisoners.
The MoJ average cost there is £13,200 per place, less than half the average cost of existing prison places, particularly in older facilities - some of which date back to the 18th century.
Some 83,632 inmates were behind bars as of last Friday, down from the record high of 88,179 after the summer's riots in 2011. MoJ forecasts show the population could hit 90,900 by 2018.
Plans to build a new super-prison are likely to draw comparisons to Labour's £2.9bn proposal for three 2,500-capacity "Titan" jails, which was scrapped in 2009.
Juliet Lyon, director of the Prison Reform Trust, said shutting prisons and cutting prison numbers offered "major social and economic gains".
But she warned it would be a "gigantic mistake to revive the discredited idea of titans and pour taxpayers' money down the prison-building drain".
She urged the coalition to invest in crime prevention, healthcare and community solutions to crime instead.