What title was given to Napoleon's son at his birth?

Napoleon’s son was given the title King of Rome at birth.

Born on 20 March 1811, Napoleon François Charles Joseph Bonaparte was the only legitimate child of Napoleon I and his second wife, Marie Louise of Austria. The title connected him symbolically with Rome and suggested that Napoleon’s dynasty had inherited the authority of ancient imperial rulers. He was also constitutionally the Prince Imperial of France and heir to his father’s throne.

The child’s birth was politically important because Napoleon had long wanted a legitimate son to secure the succession of the First French Empire. His birth was celebrated throughout France, and the title King of Rome was used from the beginning, even though he never ruled Rome. After Napoleon’s abdication, the boy was briefly treated by Bonapartists as Napoleon II, Emperor of the French, but he never exercised power.

A common mix-up is Duke of Reichstadt, the Austrian title he received from his maternal grandfather in 1818. That was his later title in Vienna, not the title given at birth. He died in 1832 at age 21 and is often remembered by the nickname L’Aiglon, or “the Eaglet.”