There was probably a wooden castle here during the 1100s.
The first stone building was the great hall built around 1200.
The towers, gatehouse and curtain walls were added in the period 1219 when Hubert de Burgh, the Justice of England, held it.
Henry III, having dismissed de Burgh, took over Grosmont but was attacked here by the Welsh in 1233 while his army were sleeping in tents outside, and lost all his baggage and horses.
The castle (with Skenfrith and White Castle) became part of the earldom of Lancaster, held by Henry͛s son Edmund from 1267.
The living quarters, including ‘Eleanor’s chimney’, were built in the 14th century. Edmund’s grandson, Henry of Grosmont, was made Duke of Lancaster by Edward III.
Henry͛s grandson became Henry IV in 1399 and the duchy and the castle again became royal property.
In 1405 Owain Glyndwr burnt some houses in Grosmont in the course of a battle with the royal army on the banks of the Monnow – recorded by Prince Hal, son of Henry IV (born in Monmouth) and the future Henry V.
Thereafter the castle declined and in 1645, during the Civil War, Charles I spent the night in Grosmont but not at the castle!