A ha ha is a sunken ditch which serves as a boundary marker for property, allowing a continuous vista to create the illusion that the garden and landscape were one and undivided. It was a common way for landowners to keep large areas of grassland trimmed using livestock, preventing the grazing animals on large estates from gaining access to the lawn and gardens adjoining the house. There are two schools of thought as to how the term “ha ha” came to be used. One suggests it is an exclamation of shock from the unwary pedestrians who suddenly find themselves in a ditch, another that it is the reaction of any spectators who see the walker abruptly disappearing from sight. This one is an unusually long example separating what was the Royal Artillery Barracks Field from Woolwich Common. It was installed sometime around 1774 to prevent sheep and cattle, grazing while at a stopover on Woolwich Common on their journey to the London meat markets, from wandering onto the Royal Artillery gunnery range.