He managed to retain the loyalty of the Iranian nomadic groups in Central Asia, the Saka, the Dahae and the Massagetae.

[11] Bessus later took part in the Battle of Gaugamela against Alexander in 331 BC, where he supplied Darius III with a contingent composed of Bactrians, Sogdians, Indians, as well as his Saka allies.

[12][7] He led the cavalry on the left wing of the Persian forces, with the intention of crippling Alexander's attack on that flank.

Fleeing from the pursuing Macedonian forces, Bessus and the rebels carried Darius III in a covered wagon, reportedly in golden chains.

In order to buy some time for their escape, Bessus and his co-conspirators killed Darius III and left his body by the road.

[18] However, Bessus' empire quickly started to fall apart; Nabarzanes, accepting his hopeless position, surrendered to Alexander and was pardoned with the help of Bagoas.

Instead of making a stand, Bessus fled into Sogdia by crossing the Oxus, where he hoped to obtain aid from the Sogdians, the Chorasmians, and the "Scythians dwelling beyond the river Tanais".

[23] The Canadian historian Waldemar Heckel suggests that Bessus may have in reality not been particularly popular, and adds that his most prominent supporters had either been killed or fled.

His actions indicated that he planned to continue the administrative system of the Achaemenid Empire, which meant that the local leaders in Central Asia would be allowed to maintain their authority.

[24] At Nautaca (present-day Shahrisabz) Bessus was arrested by his Sogdian officers, who included Spitamenes, Dataphernes, and Catanes.

[28] Seeing as they are in a hopeless position, Janusipar along with Mahyar (Nabarzanes) murders Dara II (Darius III) and then attempt to negotiate with Iskandar (Alexander), eventually meeting up with him.