In 1745 a little-known German princess named Sophie of Anhalt-Zerbst married the nephew of Empress Elizabeth of Russia. Seventeen years later she overthrew her husband to become Catherine the Great, one of the most celebrated monarchs in history, turning eighteenth-century Russia into arguably the largest and most powerful state since the fall of the Roman Empire. Admired for her achievements and satirized for her personal life, she wrote the most revealing memoirs by any European ruler. She promoted radical political ideas and emphasized moderation in government. Ruthless when necessary, she charmed everyone she met, joking at private dinner parties in the Hermitage, which she had built for her own use. Determined to endear herself to the Russians, she made religious devotions in...