The first step to answering this question is to ascertain exactly what a short sword is. This is heavily subjective and dependent on the culture and era being discussed. If you were a Roman, Greek, or Spaniard during the last two centuries BCE, your conception of a "standard" (if there was even such a thing) sword was perhaps 18-24 inches in length. If you were a Celt in that same period, it was a weapon perhaps 29-37 inches in length. As these cultures came into contact, doubtless comparisons would have been made, but they would have been subjective. To a Roman, a Celtic sword would be long; to a Celt, the Roman sword would be short.

In the west, a fairly homogeneous cultural standard continues through to the High Middle Ages, with swords of a given time and place being of roughly similar dimensions. From perhaps 300 CE through to 1200 CE, most swords were (or, at least, those that survive, and are attested to in pictorial evidence) somewhere in the 30-38 inch range, with a relatively broad, straight blade, a relatively blunt point, and a short grip. These features reflect their usage. The grip is short, because it is meant to be held with one hand, while the other grasps a shield. The blade is broad and straight so that deep, shearing cuts may be delivered, generally to unarmored body parts (mail is a surprisingly good armor, but during this time period it rarely covered the lower arms, hands, legs, or feet). The point is not particularly acute, but it is enough to deliver limited thrusts. With a weapon of this nature in one's possession, it would make little sense to invest money and resources into acquiring a smaller sword; it will offer only marginal advantages in certain circumstances (close fighting), while adding additional weight and encumbrance.

This begins to really change around c. 1200. Throughout the 12th century, armor had been becoming more developed and comprehensive. The mail shirt, short-sleeved and thigh-length, and the open-faced helmet of c. 1000, had given way to a long, thigh length hauberk, long-sleeved and with integral mittens. The legs and feet were now mailed, and the head frequently protected by a helmet with a crude face guard. Against a warrior so arrayed, a straight, single-handed cutting sword was of distinctly limited utility, and thus we begin to see real specialization - and divergence - in the sword making art.

Axes and clubs had always been used as anti-armor weapons, the former to cut through it, the latter to break the bones beneath it. Maces came to replace clubs during this period as a more specialized armor-defeating weapon, but as we are specifically discussing swords, we will not discuss it further. The falchion seems to have appeared around this time, but the falchion is so different in form from the typical European swords that it is best to treat it separately. Suffice to say, it more than anything resembles a vastly oversized knife or perhaps extra-long machete, with a long, broad, curved blade, sharpened on one edge, and optimized for hacking cuts. It may have been a foot soldier or peasant's weapon.

Most importantly, though, a sword known by curators and collectors as the Oakeshott Type XII appeared at some point in the 13th century. This is really the first medieval European sword that seems to have been optimized for the thrust as well as the cut. The blade, while not much longer than earlier swords, has a more pronounced taper, going from a wide base to a significantly more acute point. Yet even with this weapon, a shorter sword is not needed. It can do nearly everything that a weapon of eight or ten less inches can do, and many things that it cannot.

This brings us to the first of the two-handed swords, what is referred to as the Oakeshott Type XIIa. This is a fairly massive weapon, with a blade some 37 to 40 inches, and a hilt of 6.5 to 9 inches, but in design basically similar to the smaller XII. It is a cut-and-thrust sword, and because it is used with two hands, the wielder gains not only more force, but better leverage for stabbing into openings, or for shearing through weak points. This weapon was in use around the turn of the 14th century, and was one of the first swords meant for use specifically against plate armor, which was first coming into use during this period. The idea would be subsequently refined, leading to more and better two-handed swords. But this is the first.

The downside to using one of these new two-handed swords is the swordsman is himself more vulnerable to attack. It was useful to have the ability to switch, as it were, to a shield and a more manageable sword if the situation required it. As plate became more developed, the swordsman became correspondingly less so, until by the late 14th century shields were virtually abandoned. Even still, the one-handed sword persisted. In peacetime, it was handier, easier to carry on one's person by way of scabbard and belt (the two-handed swords would generally have been strapped to a horse or carried in the hands); in war, it was more useful at close range, or if the larger sword had been lost or wrestled away. It had, in effect, become a sidearm, as well as a badge of rank. The new word for this sword becomes the arming sword, in contrast to the long sword. So, you could very well say that, between 1300 and 1500, it was indeed common for a warrior (a wealthy one, anyway) to carry two swords, one relatively short, and one relatively long. His sword was no shorter than the swords carried by his forefathers in the 3rd through 12th centuries (in fact, it was frequently longer), but it was short compared to the 48-60 inch longswords in use in the age of plate.

I close with links to some articles that may prove of use. They include very good photos of surviving swords, as well as fuller and more expert opinions on their origins and use.

First, the Roman Gladius, a "short" sword. http://www.myarmoury.com/feature_ironempire.html

Second, the Migration Period Germanic sword. A long sword. http://www.myarmoury.com/review_tmpl_suthoo.html

Third, the type X, the standard of the early medieval world. http://www.myarmoury.com/feature_spotx.html

Fourth, the XII and XIIa, the first real thrusting swords of European history. http://www.myarmoury.com/feature_spotxii.html

And, just because I wish to avoid confusion, the falchion. Note that it is radically different from the others. http://www.myarmoury.com/review_at_shfalc.html