During his early career, he was reportedly an obscure figure among his peers and first rose to prominence during the Cadusian expedition of Artaxerxes III in the 350s BC.

Darius is partially remembered in Iranian traditions as Dara II, the last king of the mythological Kayanian dynasty, which reflected memories of the Achaemenids.

[5] He first adopted the regnal name of Darius (Old Persian: Daraya-vahauš, "he who holds firm the good(ness)") when he ascended the Achaemenid throne in 336 BC.

He is not attested in any Persian sources and is almost completely only known from the reports of Greek historians, who portray his career as a contradiction to that of the successful Alexander the Great.

[1][9] It was probably after this promotion that Artashata married for the first time, to an unknown noblewoman, who bore him two daughters, and possibly a son named Ariobarzanes.

[1] This demonstrates that Artaxerxes III, who was highly alert on any possible relative to challenge the throne, did not consider Artashata to pose the slightest threat to him or his son Arses.

[14] In late August/late September 338 BC, the court eunuch and chiliarch (hazahrapatish) Bagoas orchestrated the poisoning and subsequent death of Artaxerxes III through the latter's physician.

[1][11] Macedonian propaganda, made to legitimize the conquests of Alexander the Great a few years later, accused Darius III of playing a key role in the murder of Arses, who was portrayed as the last king of the Achaemenid royal house.

He sent an advance force into Asia Minor under the command of his generals Parmenion and Attalus to liberate the Greeks living under Persian control.

After they took the Greek cities of Asia from Troy to the Maiandros river, Philip was assassinated and his campaign was suspended while his heir consolidated his control of Macedonia and the rest of Greece.

In the spring of 334 BC, Philip's heir, Alexander, who had himself been confirmed as Hegemon by the League of Corinth, invaded Asia Minor at the head of an army of Macedonian and other Greek soldiers.

It is told by Arrian that at the Battle of Issus the moment the Persian left went to pieces under Alexander's attack and Darius, in his war-chariot, saw that it was cut off, he incontinently fled – indeed, he led the race for safety.

Despite all these beneficial factors, he still fled the battle before any victor had been decided and deserted his experienced commanders as well as one of the largest armies ever assembled.

Many Persian soldiers died that day, so many in fact that after the battle the casualties of his forces ensured that Darius would never again raise an imperial army.

[31] Darius then fled to Ecbatana and attempted to raise a third army, while Alexander took possession of Babylon, Susa, and the Persian capital at Persepolis.

The Battle of Gaugamela, in which Alexander the Great defeated Darius III of Persia in 331 BC, took place approximately 100 kilometres (62 mi) west of Erbil, Iraq.

Darius did attempt to restore his once-great army after his defeat at the hands of Alexander, but he failed to raise a force comparable to that which had fought at Gaugamela, partly because the defeat had undermined his authority, and also because Alexander's liberal policy, for instance in Babylonia and Persis, offered an acceptable alternative to Persian policies.

[31] When at Ecbatana, Darius learned of Alexander's approaching army, he decided to retreat to Bactria where he could better use his cavalry and mercenary forces on the more even ground of the plains of Asia.

[33] Persian forces became increasingly demoralized with the constant threat of a surprise attack from Alexander, leading to many desertions and eventually a coup led by Bessus, a satrap, and Nabarzanes, who managed all audiences with the King and was in charge of the palace guard.

[34] The two men suggested to Darius that the army regroup under Bessus and that power would be transferred back to the King once Alexander was defeated.

This led to Darius being regarded by some historians as cowardly and inefficient,[39] as under his rulership, the entirety of the Persian Empire fell to a foreign invader.