The falx had a curved scythe-like blade with a long handle with a single cutting edge on the concave side of the blade.
the Falx sword, similar to a Falcata, used its forward facing curve to crack into enemy helmets or hook around shields. Both swords were famously used by Thracians, Bastarne, Dacians, and other Balkan barbarians. Romans soldiers also occasionally used both swords as a substitute for the Gladius. The Sica is a Roman sword that was inspired by the Falx.
The deep curvature of the falx's blade made it a purely offensive weapon with little defensive capabilities. Thus, it was mainly used after the enemies' ranks had been broken by long-distance attacks, with falx-wielding soldiers hacking the devastated adversaries apart.