Swords beyond dagger length were being produced from the start of the Bronze Age, but did not become common until around 1700 BCE.
Around that time some even reached medium sword length, up to more than a meter long, but it seems they were used only as "rapiers", pure stabbing weapons without a slashing function.
Bronze swords are too soft to withstand repeated heavy blows.
Iron had the potential to improve that,
but as early iron was not quench-hardened, it was but little stronger than bronze and sometimes even weaker.
Blows could be dealt with bronze and iron, but this made the swords deform and then they had to be bent back straight, often in the middle of a battle.
Other factors than the blade strength were more important in constricting sword length.
In the Bronze Age the spear was still the dominant hand weapon and the sword was just a side-arm.
The limited reach and high cost of swords kept the majority of them limited to dagger or short sword size.
During the Bronze Age, there was a gradual shift from stabbing swords to slashing ones.
Only after the invention of steel did longer swords become common, though short swords remained in use next to them.
There is a great variety in design of short swords.
Some, like the Greek kopis and makhaira, the Celtic falcata, the Nepalese kukri and the Medieval falchion are single-edged and often have concave blades.
They are used for heavy, chopping attacks.
Others, like the Sumerian khopesh and the naval cutlass, have convex edges and make slicing attacks.
The middle way is found in straight, double-edged blades like the Greek xiphos and the Roman gladius, which can be used for slashing but mostly make stabbing attacks.
The general straightness of the blade does not imply the edge should be straight too; for example the xiphos is leaf-shaped.
A special class are the Japanese short swords like the wakizashi.
War Matrix - Short sword
Late Bronze Age 1600 BCE - 1100 BCE, Weapons and technology