François Ier protégea Léonard de Vinci.

Bonjour Robert, No, it's not an error. Ier is the Roman number I (one) followed by er - it's just another way of writing 1er, the abbreviation of premier.

THE RULE: Notice that cardinal numbers (deux, trois, quatre...) are used for royalty where ordinals (second, third, fourth...) are used in English, except for 1st = Ier / premier.

The pronunciation in "François Ier protégea Léonard de Vinci" and "J'ai bu un tiers de la bouteille." is not as clear as the pronunciation of other speakers in this lesson.