Arthur Waldron

Although what was new in 1990 has percolated into every other book by now, this is splendidly written and conceived.

In very short: walls were a matter of politics. He examines the politics. Ming in the main, but Ming make a typical story and similar debates went on in other eras. In fact the old debates - offence/defence, treaty or hostility - cycled and cycled... He tells you that.

Certainly where to go for an introduction to walls.