I agree with Danny Alcatraz; Movies are terrible examples of how medieval combat worked. Blades snapping from a single blow from another blade just *did not happen*. Blades snapping after hours of combat when someone struck a rock hard, or wedged it into a tree stump and pulled just the wrong way to free it, that might happen.
More often, swords would become bent and have to be straightened, usually accomplished on the battlefield by bracing the sword against the ground and stepping on the bent portion until the sword was usable again. Soldiers and knights were trained to parry with the flat of the blade specifically to avoid chipping the edge.
Swords were flexible but also quite easy to brake. I cant comment on if it would break when two fighters would meet in the bind, but their are midevil manuscripts that show knights breaking an opponents weapon under his foot.
Also about the parry, I don think its as simple to say that all or most parried with the flat.
In German longsword 14 century you might parry with the flat, but the basic tenet it so kill the other guy with a very direct and effective attack. when you swing, the opponent might block you, but your more worried about the kill. It helps to meet on the weak of the blade though. that saved the swords stress, but the swords tend to meet edge on edge quite often.
German longswords tended to be very wide and beefy.
Now Italian longsword fighting, I think you would see alot more parrying in general, and i know of one move in particular that you parry with the flat of the blade.
Italian longswords tended to be thinner and lighter (but still very much a longsword)
Different schools, periods, and nations fought differently from each other, and makes things very complicated. and the sword styles varied throughout history.
