Wikipedia
The Agrianians ( Ancient Greek: Ἀγρίανες, Agrianes) were a Thracian or a Paeonian- Thracian tribe whose country was centered at Upper Strymon, in present-day westernmost Bulgaria, and also held areas of southeasternmost Serbia, at the time situated south of Sofia next to the Dentheletae and close to Pangaeum. The only writer who describes the Agrianes as Thracians is Theopompus.
In the times of Philip II, the territory of the Agrianes was administered by Pella. They were crack javelin throwers and an elite unit of Alexander the Great's light infantry, who fought under the command of General Attalus.
They fought light; they carried a bundle of javelins into battle and wore no armor or helmets, perhaps not even shields. Alexander made heavy use of them and every time he dispatched a flying column, the Agrianians were always included. They were expert fighters in mountainous terrain where the phalanx was impracticable and mobile enough to use when speed was essential. Being an elite unit of the light infantry, they often formed up with the hypaspists battalion and the companion cavalry on the right wing of the army.
They are first mentioned regarding the Megabazos' campaign in 511 BC. In 429 BC they were subject to the Odrysian kingdom and later, as early as 352 BC, they became allies of Philip of Macedonia.
At the Battle of Gaugamela (331 BC), they numbered 1,000 men. They fought under king Langarus with the Macedonians against the Triballians in 335 BC and succeeded in protecting the lands of Alexander and were thus rewarded with the right to govern themselves, a move that led to a long-lasting and most reliable alliance. During the time of the Seleucid Empire, a crack unit of Antiochus' Agrianes was brigaded together with Persians at Raphia. Contingents from the Agrianes and the Penestae, numbering 800 and 2,000 men respectively, were a part of the garrison of Cassandreia at the time of the Third Macedonian War.
The ethnonym is of Indo-European origin (from *agro- "field" (cf. Lat. ager, Gk. ἀγρός agros, Eng. acre).