Buns aside - the vitrefied walls would effectively deflect any pointed projectile such as 4W's javelins, fire-arrows etc as well as grapples (dont know enough about IA tech , so if a grappling hook is an anachronism - indulge me!).

As far as cooking up the builders, that would suggest that pre-attack vitrification may have been a process used to render the ramparts unscalable.

Is there any evidence of any combustible materials being discovered at the sites?