When people think of the short
sword in general they often think of the Roman
gladius, a highly-effective stabbing and piercing
weapon made famous by the
legions of
Rome. However, it was not the first short
blade of renown and in fact it was another short sword that Rome's early
republic was built upon -- the greek xiphos.
In Greek, the word "xiphos" literally translates as "sword", which should speak to the regard of this particular weapon even though it wasn't the only actual sword used in the time period.
The xiphos was a short, straight, double-edged blade that generally ranged anywhere from 19 to 25 inches (48 to 65cm) in length. The most-distinguishable characteristic of the xiphos is that the blade itself is leafed -- in other words its width slightly increases as you go up from the hilt, before tapering back off to a point at the blade's tip, thus giving the blade a shape similar to a leaf. This design provided more impact at the crucial point on the blade where most of the cutting and slashing motions would be targetted, moving the center of gravity closer to the sword's point.
Unlike the Roman gladius which was mainly used for stabbing and thrusting, the xiphos was a versatile weapon that could also be used for slashing and even chopping to a certain extent (although for chopping nothing compared to the outwardly-curved kopis), and it was highly-effective when used to thrust and stab between the joints in an opponents's armor.
While the Greek hoplite's primary weapon was the spear, due to the tight phalanx combat of the day, the secondary weapon of choice was often the xiphos, especially amongst officers. While the average hoplite might have anywhere from 3 to 9 spears for use in a battle, the spears often broke and if a battle lasted very long hoplites had to rely upon the xiphos to win the day. The Spartans in particular were famed for their use of the xiphos even though records indicate that probably not a lot of training focus was spent on the sword and its use. This may partially be due to the fact that many Greek-on-Greek phalanx battles tended to be spectacular but brief. At any rate the xiphos was still a fairly simple weapon and could be effective even in untrained hands.
The xiphos also apears to have been even used on horseback, even though the famed Greek historian and tactician Xenophon recommended that mounted combatants use the curved "makhaira" (a curved sword similar to the kopis except curved inward, not outward).
It is worth noting that some evidence points to Spartan hoplites using even shorter versions of the xiphos (only around a foot, or 30 cm, long) by the time of the Peloponnesian War. It's quite possible these were intended to be used more like the gladius of later years. However, none of these variants seemed to have survived.
One thing many people forget is that while Rome was still expanding its influence over the Italian peninsula the Roman legions did not exist -- Rome instead used classical Greek phalanx combat with the typical bronze armor, shields, and spears that go along with that style of combat. And naturally that fighting style meant that the xiphos and very minor variations of it were the secondary weapons of choice still for the early Roman armies. It wasn't until sometime in the second century B.C. and the onset of the Punic Wars (particularly the Second) when Rome had abandoned the phalanx in favor of the manipular legion that the xiphos fell into disuse in favor of the famed gladius. The armies of Carthage however appear to have still used variations of the xiphos on through those same Punic Wars.
Perhaps one of the biggest faults with the xiphos lay not in the weapon itself, but in the lack of training on how to use it. Most hoplites of the era were drilled tirelessly on the shield wall and spear aspects of phalanx combat, leaving very little training towards the use of the xiphos once combat had degenerated largely into a chaotic melee with no distinguishable lines.
In the end the xiphos was not a perfect weapon. Its use required that the combatant get in very close to his enemy, and the bronze armor and shields of the day were not exactly optimized for combat with short swords. It was however a well-balanced, simple, effective blade for a secondary weapon, and for that reason it saw many centuries of use. Today the xiphos is amongst the most-prized of the ancient swords for a collector, and remains one of the finer ancient weapons.
Sources:
http://www.myarmoury.com/feature_ironempire.html
http://www.hoplites.co.uk/pdf/hoplite_swordsmanship.pdf
http://www.nationmaster.com/encyclopedia/Xiphos
http://en.wikipedia.org/wiki/Makhaira