Captured officers once won freedom simply by giving their word
In eighteenth-century Europe, a captured officer could hand over his sword, swear as a gentleman not to escape, and receive comfortable lodgings and the run of the town. Swear never to fight his captors again and he might be sent home. That custom, called parole, marked a long shift in how enemies held in war were treated.
For most of history, captives faced death or slavery. Rome's early gladiators included prisoners sorted by origin as Samnites, Thracians or Gauls, and Christian and Muslim navies alike chained captured men to galley oars; the victory at Lepanto in 1571 freed 12,000 Christian rowers from Ottoman ships. Noblemen were the lucky exception, since their families could pay ransoms scaled to their rank. Mercy came in individual acts. In the fourth century Bishop Acacius of Amida sold his church's gold and silver vessels to ransom Persian prisoners and send them home, and was later made a saint for it.
Between the sixteenth and late eighteenth centuries, European states took control of the process. Prisoners stopped being the private property of whoever seized them and became the responsibility of governments, which regulated surrender through officers negotiating for whole units. The Peace of Westphalia in 1648, ending the Thirty Years' War, set the rule that prisoners go home without ransom once fighting stops. Treaties called cartels arranged swaps of equally ranked men even mid-war, easing both crowded prisons and shortages of trained personnel.
The first purpose-built camp opened at Norman Cross in Huntingdonshire in 1797 for captives from the wars with Revolutionary and Napoleonic France. It held around 5,500 men on average, peaking at 6,272 in April 1810. Intended as a model, it served food at least as good as locals ate, and senior prisoners inspected deliveries. About a hundred high-ranking officers lived on parole in nearby Peterborough.
The system could break down. In the American Civil War captives were initially paroled into camps run by their own side until formally exchanged, but swaps broke down in 1863 over the Confederacy's refusal to include captured black soldiers in any swap. Ulysses Grant declined to restart the cartel in August 1864, and roughly 56,000 of 409,000 prisoners died in captivity during the war.
Source: Prisoner of war
