"During the Middle Ages, castles kept improving, they kept improving as weapons of attack got better, and tactics was this eternal balance between attack and defense."
"Heave!"
Two hundred years before cannon appeared in Europe, chroniclers make reference to what appears to be the ultimate 13th century's siege weapon: an ingenious new form of heavy artillery that flung huge stone balls with such destructive power that castle walls were reduced to rubble. But no ancient weapon of this type has survived. Were such claims gross exaggerations, or did such a weapon really exist?
To answer these questions, NOVA brings together a team of experts in medieval warfare, who believe they know the secret.
"It's chaos, it's Wednesday I think, I don't have a clue whether or not we'll finish."
Their task, to build siege machines capable of destroying a castle wall at a range of about 200 yards.
"Well, I think that the thing will smash it up, nicely yeah."
With just two weeks to meet the challenge, a siege mentality quickly sets in. No modern builders have ever managed to do this before.
"...balance. Once I got it in, the whole thing could twist and tip quite alarmingly."
"one more draw, one more draw."
This interplay between defenders and siegers, it's still up in the air, we could still take it, then again we could fail. It's sort of "in the lap of the gods".