A kestros or kestrophedrone, also known as a cestrus or cestrosphendone, is a specially designed sling

Sling (weapon)

A sling is a projectile weapon typically used to throw a blunt projectile such as a stone or lead "sling-bullet". It is also known as the shepherd's sling....

 that is used to throw a heavy kind of dart

Dart (missile)

Darts are missile weapons, designed to fly such that a sharp, often weighted point will strike first. They can be distinguished from javelins by fletching and a shaft that is shorter and/or more flexible, and from arrows by the fact that they are not of the right length to use with a normal...

.

The dart would typically consist of a heavy metal point approximately nine inches (22.9 cm) long, attached to a shaft of wood, typically twelve inches (30.5 cm) long, and fletched

Fletching

Fletching is the aerodynamic stabilization of arrows or darts with materials such as feathers, each piece of which is referred to as a fletch. The word is related to the French word flèche, meaning "arrow," via Old French; the ultimate root is Frankish fliukka...

 with feathers or the like to provide stability of flight.

History

The kestros is mentioned in the writings of Livy

Livy

Titus Livius — known as Livy in English — was a Roman historian who wrote a monumental history of Rome and the Roman people. Ab Urbe Condita Libri, "Chapters from the Foundation of the City," covering the period from the earliest legends of Rome well before the traditional foundation in 753 BC...

 and Polybius

Polybius

Polybius , Greek ) was a Greek historian of the Hellenistic Period noted for his work, The Histories, which covered the period of 220–146 BC in detail. The work describes in part the rise of the Roman Republic and its gradual domination over Greece...

. It seems to have been invented around 168 BC

168 BC

Year 168 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Macedonicus and Crassus...

. and was employed by some of the Macedon

Macedon

Macedonia or Macedon was an ancient kingdom, centered in the northeastern part of the Greek peninsula, bordered by Epirus to the west, Paeonia to the north, the region of Thrace to the east and Thessaly to the south....

ian troops of King Perseus in Third Macedonian war

Third Macedonian War

The Third Macedonian War was a war fought between Rome and King Perseus of Macedon. In 179 BC King Philip V of Macedon died and his talented and ambitious son, Perseus, took his throne. Perseus married Laodike, daughter of King Seleucus IV Keraunos of Asia, and increased the size of his army...

. The description is quite confusing:
The exact construction of the Kestrosphendone remains somewhat mysterious. However, experimental reconstructions based on the available information have resulted in quite spectacular results. Nonetheless, the Kestrosphendone did not stand the test of time and seems to have been abandoned quite quickly. The fundamental purpose of this weapon seems to have been to develop a sling shot with the penetrative power of a point. If so then a lighter version of this weapon, the plumbata, persisted into late antiquity. In this weapon the wooden shaft gave nearly the same mechanical advantage as a sling. In effect each sling bolt came with a one time sling.

Another way of obtaining a one time sling was to fix a string to a slingstone made of lead. There is evidence for this variation at the Battle of Fucine Lake

Battle of Fucine Lake

The Battle of Fucine Lake was fought in 89 BC between a Roman army and a rebel force during the Social War. Lucius Porcius Cato was the leader of the Roman army at this battle. The consul Porcius Cato was defeated and killed while storming a Marsic camp in winter or early spring.There is an...

in 89 BC.