How many Musketeers were there in the title of the book by Alexandre Dumas?

The Three Musketeers (French: Les Trois Mousquetaires) is a historical adventure novel written in 1844 by French author Alexandre Dumas. It is in the swashbuckler genre, which has heroic, chivalrous swordsmen who fight for justice.

Set between 1625 and 1628, it recounts the adventures of a young man named d'Artagnan (a character based on Charles de Batz-Castelmore d'Artagnan) after he leaves home to travel to Paris, hoping to join the Musketeers of the Guard. Although d'Artagnan is not able to join this elite corps immediately, he is befriended by three of the most formidable musketeers of the age – Athos, Porthos and Aramis, "the three inseparables" – and becomes involved in affairs of state and at court.