Richmond Castle was founded soon after the Norman Conquest by Alan Rufus, a Breton supporter of William the Conqueror who received extensive lands in northern Yorkshire. Construction began around 1071 on a rocky height above the River Swale. Stone walls and buildings appeared unusually early, enclosing a great hall, chapel, service ranges, and defensible approaches. The castle anchored the Honour of Richmond, a vast lordship whose estates and obligations extended well beyond the town that developed outside its gates.

Alan's successors, the counts of Brittany, expanded the fortress. The great keep was built in the twelfth century, probably under Earl Conan, providing a monumental tower for residence, storage, and display. Richmond's lords moved within international aristocratic networks linking England and Brittany, while constables and stewards managed the estate in their absence. Kings periodically took control when inheritance or loyalty was disputed. The castle's northern position also made it useful during tensions with Scotland, though it was never simply a border outpost.

By the later Middle Ages Richmond was less frequently occupied by great lords. Administrative functions continued, but halls and chambers deteriorated. The Crown and later owners used parts of the site for storage, justice, or local government, while the town grew around it. Military technology and changing patterns of noble residence made the steep fortress inconvenient. The intact keep remained a landmark even as the enclosure lost roofs and internal buildings, giving later visitors an incomplete impression of the once-crowded household.

The army returned in the nineteenth century, building barracks beside the medieval ruins. During the First World War, cells in the castle held conscientious objectors, including the men later known as the Richmond Sixteen. They refused combatant service on religious and moral grounds, were transported to France, and faced death sentences commuted to imprisonment. Graffiti left in the cells preserves their voices and turns the castle into evidence for modern conflicts over military authority, individual conscience, and compulsory service.

Richmond Castle is now cared for as a historic monument, with conservation encompassing Norman masonry, later military structures, and the fragile cell inscriptions. Interpretation must connect the power imposed after 1066 with the discipline exercised during industrialized war without treating the two periods as identical. The castle's long history includes Breton lordship, royal custody, estate government, decline, barracks, and imprisonment. Its surviving keep dominates the landscape, but documents, archaeology, and graffiti reveal institutions and individuals who left less monumental traces.