Walls are generally a poor idea militarily. The very considerable resources needed to build and maintain it are usually better spent on other military options.
A linear wall is useless if breached at any point. Whereas a series of strongpoints can be held and used as bases for a counterattack.
“A linear wall is useless if breached at any point. Whereas a series of strongpoints can be held and used as bases for a counterattack.”
True, if the threat is purely military. But some studies of The Great Wall and Hadrian’s Wall suggest that these barriers served as a kind of “customs station” where tariffs could be assessed and the like. In this way these ancient walls served more like a modern border crossing.