“The other kind of boundless garden is not a geometrical figure at all. This English kind has no obvious beginning or end and the bounds are confused on all sides, so that for this garden an un-wall had to be invented, which performs the physical functions without having the visual value of a wall. The ha-ha or sunken fence is an English joke on law and order that exercises real constraint with the English deviousness and we can almost imagine a simple person stumbling into these sophisticated gardens without realising that he is in a garden at all, like someone who misses an irony.”

Eccentric Spaces by Robert Harrison (1977).