Scythian campaign of Darius I

The Scythian campaign of Darius I was a military expedition into parts of European Scythia by Darius I, the king of the Achaemenid Empire, in 513 BC. The Scythians were an East Iranian-speaking people who had invaded Media, revolted against Darius and threatened to disrupt trade between Central Asia and the shores of the Black Sea as they lived between the Danube and Don Rivers and the Black Sea. The campaigns took place in parts of what is now the Balkans, Ukraine, and southern Russia.

Source: Wikipedia — Scythian campaign of Darius I (CC BY-SA 4.0)