Leonardo da Vinci’s 33-barrel rapid-fire weapon design is commonly called an organ gun.
The design arranged many small cannons in parallel rows, resembling the pipes of a musical organ. The barrels could be fired in sequence, allowing one row to discharge while another was being prepared.
Leonardo’s purpose was to improve the practical rate of fire of artillery. He recognized that repeatedly loading a single cannon was slow, so a grouped arrangement could produce a continuing series of volleys.
The organ gun was a concept rather than a standardized firearm adopted by an army. It is sometimes called a “machine gun” in popular descriptions, but that modern label can obscure the fact that the weapon used separate cannon barrels and gunpowder charges.