American researcher Richard Wilmer Rowan devoted his work to the history of intelligence services, covering three millennia of work by secret agents from different countries. The author examines the practice and evolution of surveillance from royal chambers to double-dealing associations, from autocratic conspiracies and intrigues to state forms of the "back ladder". Being not only a weapon of tyranny and the protection of governments and armies, but also an underground method of international struggle, the secret services used police surveillance and secret emissaries in the Byzantine Empire, and in medieval Asia... and under Napoleon, and right up to the Entente and modern times, elevating political espionage from craft to art.