I'm shocked when I see pictures of the tangs on historical swords. Many of them seem incredibly small. Even modern reproductions that use decent sized tangs like these...
http://www.albion-swords.com/bareblades.htm

...still seem very small and breakable to me. I'd think that under hard use they would bend or break often. I know many modern knife makers of high quality knives use a "hidden tang", I believe it's called, where the tang is the same width as the grip itself, just with slabs over it. What would have been the downside of making sword hilts with tangs like this? it would obviously add a slight amount of weight, but not much, and it would seem far more sturdy.

I've seen a few historic blades that used this design, but none of them seemed like the steriotypical "medieval aged sword".

Tension within the whole hilt assembly helps keep the tang from being over strained. Besides that, lets say the tang of a sword is 3/4 to an inch and 1/4 odd inch wide properly tempered. The amount of force necessary to actually break the tang is almost like running it over with a truck. Repeated blows over time can weaken it (especially if there is a low quality weld or flaw that could create a stress crack) and it could eventually break. The yield strenth of most steel types from low carbon to high carbon is in the range of 30,000psi to 70,000+ depending on the specific steel type. its some pretty strong stuff. And there are European designs that use a scale grip on a wide tang (The messer immediately comes to mind) http://pics.myArmoury.com/view.html?messer_kit01.jpg

Actually many medieval swords had soft tangs which could possibly bend but were very unlikely to break. But, as already said, tension of the grip assembly keeps the tang from bending.

Many medieval swords (especially later ones) had thicker tangs than most normal reproductions. While most reproduction swords are about 6mm (1/4") thick authentic swords could be as thick as 8mm at the base of the blade. And many earlier swords that were thinner had pretty wide tangs.

Also one should keep in mind that people did not understand the process of heat treatment very well. Some swords were a total crap by modern standards. Blades were far more likely to break than tangs. And even bent tang does not render the sword useless.

Also, "hard use" may not have been nearly as hard as you might think! Swords were not meant for trying to smash shields apart or cutting horses in half or chopping fire wood. You really don't need much force to lay flesh open to the bone, so the average stroke didn't have to be full-force. So even if it was blocked, the tang wasn't likely to suffer.

Bottom line, those tangs must have worked well enough, or the ancients would not have kept making them that way!

Matthew

Some tangs were very wide, others very thick. Some larger seaxes had the same full width tangs seen on japanese swords and Tantos, like the Battersea Seax. Others were thin, at times surprisingly so.

The albion line is known for its durability, these blades can cut up the rims of steel oil drums and stand up to rather extreme "cruel and unusual" punishment as seen in their testing videos. Seems to me these tangs are wide enough, at least as long the grip assembly is made the right way.

The weak point of a tang is the intersection between it and the blade. It really only needs to be wide there, or alternatively intersect with a rouning instead of a sharp corner as that is really what makes it liable to break. Another solution is to fatten it at that spot like you see in the Gladius blades in the link.
The rest of it need to be made softer than the blade temper but can be fairly thin as long as there's enough cross section for a strong peen to be made.

Aleksei makes a good point also, some swords were just crap.
Others were made as durable as possible within the knowlege and skillset the smith possessed, sometimes a customer may have requested a heavier than needed tang, if his/her sword broke there in the last battle and they never want to experience that again.
My theory about viking age seaxes that have full width tangs is that they were intended to work double as an axe or, especially considering some huge and/or more massive than regular sword seaxes, made to bash heavily armoured opponets senseless with brute force and built to that purpose. Just a theory though of course.
Another theory would be that just like japanese swords, the iron used for seax-making was of poorer quality than that of "real" swords. So the tang had to be made thicker than usual to compensate. Unless you were using sword grade metal. That would explain why some seaxes have thin tangs while most have thick tangs. A combination of both reasons is certainly also possible.

Thanks for the responses all! The differing qualities of metal and treating process was something I hadn't considered. I knew the messers had full tangs, but it didn't make sense to me that the more typical sword designs did not. It still seems to me that if you could avoid any possible breaking or bending by simply adding a very small amount of weight, why wouldn't you? But as you said, if it didn't work, they wouldn't have done it for centuries I suppose.

What about guilds?

From what I understand, (and I'm just a guy with a hobby, not a scholar ) If it had a wide tang and slab handle then it was a knife? And if you are in the knife makers guild then you couldn't sell swords? Maybe?

Or dynamics?

Having a narrower tang with a pommel peened to it means you can use the weight of the pommel to adjust the harmonics of the sword? Different weighted pommels would allow a smith to fine tune the dynamic properties of the sword?

Ay's or Nay's?

There is this Spotlight Topic that also had a discussion about tang size that has a few interesting posts to read:
http://www.myArmoury.com/talk/viewtopic.php?t=5255

I'm surprised no one has mentioned economics. Steel was much more expensive before Mr. Bessemer patented his furnace in 1855. In general, no more steel or iron would be used than necessary for the purpose at hand.