The Praetorian Guard and Varangian Guard: The History of the Elite Soldiers Who Protected the Roman and Byzantine Emperors

In the late 2nd century B.C., Gaius Marius made the army more professional and helped propel Rome's expansion, but those same reforms eventually made the legions fiercely loyal to their individual generals rather than the state, which would make Caesar's seizure of power possible and bring about the dawn of the Roman Empire.

Naturally, having military units who were only loyal to individuals also made an imperial bodyguard possible, and few institutions in the long and turbulent history o...