[decimon]

Why in heaven would you need a 43-foot-thick curtain wall, before the invention of cannons?

That's a long way to throw a spear? The wall are of mud brick so maybe the thickness was needed to keep them from digging through. As you've guessed, I don't know.

[blam]

"The wall are of mud brick so maybe the thickness was needed to keep them from digging through."

That's my guess too. Anyone digging could be dealt with before they could dig through.