Monmouth`s Regimental Museum tells the story of the Royal Monmouthshire Royal Engineers. It is housed in a 19th century wing of Great Castle House. For two centuries a militia regiment, it became a reserve regiment in 1877. The museum covers the militia system, the Dukes of Beaufort, and various regimental distinctions. There are archaeological exhibits, and displays about the early defences of Monmouth, the Home Front and recent wars. Behind the museum is a small garden with a selection of plants grown in medieval times.