The Sarmatians - one of the many nomadic groups to emerge from the great Eurasian Steppe - crossed the Don in about the 3rd century BC to displace their western neighbours, the Scythians, in the lands north of the Black Sea. Later they burst into Asia Minor and Rome's Danube provinces, becoming famous for the prowess of their lance-armed cavalry - first as enemies, and later as allies of Rome. They influenced Rome's adoption of heavy armoured cavalry, and in Roman service they were even posted to Britain. Drawing upon a wide reading of Classical authors and of Russian archaeological...