The Marshalsea had operated in Southwark in one form or another since at least 1373. The second Marshalsea, the one that mattered for Dickens, was built in 1811 on the site of an old white-stone palace whose history reached back to medieval times. It was a small place, only ten yards wide and thirty-three yards long, divided into eight three-storey houses containing fifty-six rooms in all. Most of the people imprisoned there were debtors, owing modest sums that they could not pay - a tailor in arrears with his rent, a clerk who had borrowed from the wrong neighbour, a widow whose husband had left her his debts. Records from 19 April 1826 show 105 debtors held in the prison; 99 of them had been there less than six months. The Marshalsea was not a place where people languished for decades. It was a place where people lost months of their lives over sums it would take a year of wages to repay.

On arrival, new prisoners were expected to pay a sum called garnish, a donation to the prisoners' committee that allowed access to the snuggery, the communal room where water could be boiled, candles bought, and newspapers read. The amount was five shillings and sixpence in 1815, rising to eight shillings and sixpence by 1833. Women paid less. Those who could not pay had their names written up in the kitchen and were sent to Coventry by the other prisoners. After paying, the new arrival was issued a chum ticket telling them which room they shared and with whom. Sometimes a new prisoner walked the yard for three nights waiting for a chum to be found, while already being charged for the room. The committee, made up of nine debtors and a chair (a post that John Dickens himself held), levied fines for offences ranging from singing obscene songs after midnight to defacing the staircase to drawing water before it had boiled.

It is important not to read the Marshalsea as a Dickens character. Real people lived there. Mothers gave birth in cells because the prison doctor refused to attend to wives unless paid separately. Children, sometimes a dozen at a time, lived inside with their parents and ran in the small yard, playing among the men. Women and men mixed freely - the prison was less segregated than nominally outside society - and visitors came and went without being asked who they were. The anonymous 1833 eyewitness described, with horror, women in constant moral danger; modern readers may see something more like a community that, surrounded by stone walls, simply continued the lives it had been living. Smugglers in the Admiralty section consorted with debtors. Wives ran small businesses from cells. Children walked through to the chapel. The Marshalsea was full of people whose lives had been suspended, not erased.

Charles Dickens visited what was left of the Marshalsea in May 1857, in the final weeks of writing Little Dorrit. He wrote in the preface that he had walked through the gates not certain whether anything was still standing. "I found the outer front courtyard, often mentioned in this story, metamorphosed into a butter shop; and then I almost gave up every brick of the jail for lost." He kept walking. Off Angel Court, down what is now called Marshalsea Place, he recognised the great block of the former prison, the rooms he had walked through as a frightened twelve-year-old, the very paving stones of the yard. The novel, which appeared in monthly parts between 1855 and 1857, took the prison as both setting and metaphor: Amy Dorrit, born inside the walls, becomes the moral compass of a society in which everyone is in debt of one kind or another. Imprisonment for debt was finally outlawed in England in 1869, except in cases of fraud, and by the 1870s the Home Office had demolished most of the prison.

One section survives. The southern boundary wall of the Marshalsea, separating the prison from St George's churchyard, still stands along an alley called Angel Place, just off Borough High Street. The library at 211 Borough High Street, run by Southwark Council, occupies the prison's central footprint. On the garden side of the surviving wall is a plaque from the council and a paving stone with information about John Dickens. The Cuming Museum, when it was open, held one of the prison's pumps. The Dickens House Museum holds one of its windows. To stand in St George's garden on a winter afternoon, with traffic noise floating in from the high street and the wall on your left, is to feel the boundary between what once was and what is built over it. "Whosoever goes into Marshalsea Place," Dickens wrote, "will stand among the crowding ghosts of many miserable years." The ghosts are still there. So is the wall.