In classical era Greece, the most powerful war machine the Greeks had was the phalanx. Rows upon rows of armored hoplites, each carrying a spear that sometimes reached 30 feet long. If you have difficulty imagining this, imagine a large block, with about forty 30-foot long spears protruding from the front.
But imagine if this block of bristles was penetrated, say by a cavalry charge hitting them from the back or flanks. The hoplites cannot turn around and use their spears; they are way too long to be used effectively. The formation has been broken; body mass is no help any more. So what do the hoplites do? Pull out the secondary weapon, the Kopis.
The Kopis is basically a machete, a blade about 2-3 feet long, with a blade that curves inward towards the edge. The climax of the blade width is about 2/3rds of the way towards the point, the optimum impact area. The grip was often made with an overhook at the pommel, and sometimes a chain across the knuckles to keep the sword with the user. This thing was deadly. Figures on ancient pottery often showed the warriors raising the Kopis well behind their heads, for optimum striking force. Even if the Kopis did not succeed in piercing armor, it could almost definitely kill the person wearing it from the concussion alone. Even if it didn’t kill the person, he’d at least walk or run away from that fight with a broken arm and a job for the armorer.
Some Kopii were cast from bronze, but once iron became available warriors reverted to that, as iron is much tougher and had less chance of breaking under the incredible force.
Interestingly, there is another sword, called the Falcata, that was practically the exact same
sword as the Kopis, just was of Iberian, not Greek origin. No one really knows who came up with the design first (I’m personally rooting for the Greeks). There is another weapon similar to the Kopis and Falcata, called the Kukri, of Indian origin, but is only about half the size of the Kopis or Falcata.