Once Darius had reached the Danube, he crossed the river and campaigned against the Scythians, after which he returned back to Anatolia through Thrace and left a large army in Europe under the command of his general Megabazus.

The last endeavours of Megabazus included the conquest of the area between the Strymon and Axius rivers, and at the end of his campaign, the king of Macedonia, Amyntas I, accepted to become a vassal of the Achaemenid Empire.

In the interior, the Western border of the satrapy consisted of the Axius river and the Belasica-Pirin-Rila mountain ranges till the site of modern-day Kostenets.

The importance of this satrapy rested in that it contained the Hebros river, where a route in the river valley connected the permanent Persian settlement of Doriscus with the Aegean coast, as well as with the port-cities of Apollonia, Mesembria and Odessos on the Black Sea, and with the central Thracian plain, which gave this region an important strategic value.

[5] Once the Ionian Revolt had been fully quelled, the Achaemenid general Mardonius crossed the Hellespont with a large fleet and army, re-subjugated Thrace without any effort and made Macedonia full part of the satrapy of Skudra.

Thanks to the Thracians co-operating with the Persians by sending supplies and military reinforcements down the Hebrus river route, Achaemenid authority in central Thrace lasted until around 465 BCE, and the governor Mascames managed to resist many Greek attacks in Doriscus until then.

Around this time, Teres I, the king of the Odrysae tribe, in whose territory the Hebrus flowed, was starting to organise the rise of his kingdom into a powerful state.