James Bond may have won the hearts and wallets of audiences world-wide—“Spectre,” the latest movie in the series, opens Friday after shattering box-office records in the U.K.—but armchair experts have always grumbled that Ian Fleming’s world of spies is too exciting to have any relationship to reality or history.

The critics are wrong. Fleming, who died in 1964, packed his books and plots with real historical allusions, beginning with the secrecy classification “for your eyes only.” The origins of the term go back to the Mesopotamians.

The oldest known classified document is a report made by a spy disguised as a diplomatic envoy at the court of King Hammurabi, who died around 1750 B.C. in Babylon. The spy smuggled the object—marked “This is a secret tablet” on the front—to his handlers in the Kingdom of Mari. Shortly after being found in the 20th century, the tablet and its translation went missing, vaulting it to the top rank of wanted secret files.

The spymasters of the classical world were constantly sending and intercepting secret messages, with the ancient Greeks being the first to use flag signals. But, as spy agencies today know only too well, a communications department is useless without field operatives.

Women have always been extremely effective spies. The femme fatales and female assassins who make Bond’s life so difficult were not a figment of Fleming’s imagination. Every country has its heroines, like Virginia Hall (1906-1982), the much-decorated American World War II spy who despite losing a foot played a leading role in the French Resistance. But their actions have rarely been recorded.

One exception can be found in “Arthashastra,” the ancient Sanskrit treatise on statecraft by the Indian philosopher and teacher Chanakya (around 350-275 B.C.). Like Machiavelli, Chanakya was thoroughly pragmatic about means and ends. His advice on secret female agents was to use them whenever possible, such as to kill a rival “with snakes, poison, fire or smoke while he is asleep in a secluded place.”

The “honey-trap”—the weapon of seduction that the Bond franchise has used at every possible occasion—can play a key part in real espionage. The best spies have always known how to mix business with pleasure. In between his countless seductions, Giacomo Casanova (1725-1798) translated “The Iliad,” helped run the French lottery, hobnobbed with the aristocracy and spent the 1770s as a spy for Venice. He even had his own version of Moneypenny, the love-struck secretary at Bond’s home offices, in the form of housekeeper Francesca Buschini, whose devotion Casanova repaid with cavalier disregard.

As for archvillains, every Bond enthusiast knows that the worst are the heads of shadowy organizations. One of the first spies to identify the phenomenon was the notorious con man and MI6 agent, Sidney Reilly, presumed killed in Russia in 1925. Reilly always insisted on an invisible global threat he called the “Occult Octopus.” Although Fleming, a former intelligence agent himself, denied that Reilly was an inspiration for Bond, the symbol of Spectre, Fleming’s fictional crime syndicate, just happens to be an octopus.

Access to the truth is presumably on a need-to-know-basis.