Coldbath Fields was a large prison in the Clerkenwell area of London, and was also known as the Middlesex House of Correction or Clerkenwell Gaol. It was orignally founded during the reign of James I (1603–1625), although the prison was completely rebuilt in 1794 and extended in 1850.
Coldbath Fields was renowned for the harshness of its punishments, including enforced silences using a regime known as the ‘silent system’, solitary confinement and use of a treadmill.
The prison closed in 1877 and the site was later transferred to the Post Office. Its buildings were gradually replaced and the site is now the Royal Mail sorting office at Mount Pleasant.
Further Reading (external sites).