Ha-ha Walls (Historical Marker)

Here follows the inscription written on this trailside historical marker:

Ha-ha Walls
George Washington wanted to keep farm animals away from the Mansion without obstructing visitors' views of a pastoral landscape with animals grazing in the distance. Instead of fences, he used ha-ha walls, which have a top level that is even with the Mansion's lawn, and a turf ditch on the pasture side. These hidden barriers kept livestock safely in the pasture, but their boundary was concealed.

Why were they called ha-ha walls? No one knows for sure, but some suggest that the name refers to the surprise of discovering these hidden walls, which cannot be seen until one is right on top of them!