The Skythians traced their own history back to around 1,500BCE, but the first known historical records of them as a people appear in 512BCE, when the Persian king, Darius I launched an unsuccessful raid into their territory, which roughly corresponded to the area we know today as the Crimea, and up into Ukraine and southern Russia. They were fierce warriors known for their horsemanship and archery, and the regular appearances of women warriors in their ranks prompts many historians to believe that the "Amazons" of Greek legend were in fact women of the various Skythian tribes.
The Skythians were an early Steppe nomad peoples, similar to the Huns and Mongols of later eras. They traded with the Greeks and Persians, and hired out as mercenaries. Persian kings employed Skythians to train their own troops as archers, and in the Persian battle lineup, the Skythians were lined up next to the native Persian troops, indicated the higher "prestige" they enjoyed than the mercenaries of other allied and subject nations used by the Persians.
In battle, the Skythian cavalry became known for their "wedge" formation, which was later copied by Alexander "The Great" for his Macedonian cavalry. As seen in the photo above, the Skythian Heavy Horse are deployed in a "V" formation, with the tip pointed towards the enemy, and the flanks protected by mounted archers, who provided fire support for the strike and also shielded the vulnerable flanks from counter-attack.
The "wedge" drove into the enemy line (in the photos above and below, Thracian peltasts), similar to the sharp point of a drill, splitting the enemy line and piercing deep into its ranks. The rear ranks of the "wedge", and also the supporting mounted archers, capitalized on the disorganization this caused among the defenders, eventually overwhelming them.
Skythian standards were usually made of horse-tails - white in time of peace (perhaps the fore-runner of the "white flag") and black in time of war.
The Skythians were crushed by Alexander "The Great" at the Battle of Jaxartes in 329BCE and their power declined from there. They were driven out of the Balkans by the Dacian tribes, and were eventually subdued by the Pontic king Mithridates around 100BCE. When the Romans under Julius Cesar defeated Pharnaces II, the son and successor of Mithridates, they came under Roman rule.
