Whilst comparing different ancient swords I questioned their length. They are short. An average of around 50-60cm for most, excluding some. Many cultures shared the same trait. Yes there are a few exceptions for longswords in the ancient world but thats beside the point.
Xiphos, Falcata, Gladius, Khopesh, Sica, Hallstatt and many more share the 50-60cm length. I threw away the idea of limited resource being the factor for their size. In the bronze age yes that could have been a major factor. Though in the Iron age the materials were more available, yet the size stayed roughly the same.
So heres my theory. They were all designed to be used in conjunction with a shield. Long swords are hard to use in close quarters combat. With a mass shield to shield battle a long sword is hard to swing. Obviously swinging and chopping are hard in close quarters combat but so is stabbing. The long sword is just a little too long to get around a shield. The shorter sword is then more manoeuvrable in tighter formations.
Just a rough theory.
The Stain of Rome 