A “ha ha” is a ditch which serves as a boundary between fields or properties. It is designed to be a recessed landscape design element that creates a vertical barrier while preserving an uninterrupted view of the landscape beyond. Ha has are also used in landscape design to prevent access to a garden, for example by grazing livestock, without obstructing views.
There’s also a “ha ha gate” which connects and provides access between the two areas and a “ha ha wall” which shores up the ditch.
The “ha ha” of Ha Ha Road, SE18 still exists. It flanks the Barrack Field of Woolwich Garrison.
