A culverin was a relatively simple ancestor of the musket, and later a medieval cannon, adapted for use by the French in the 15th century, and later adapted for naval use by the English in the late 16th century. The culverin was used to bombard targets from a distance. The weapon had a relatively long barrel and a light construction. The culverin fired solid round shot projectiles with a high muzzle velocity, producing a relatively long range and flat trajectory. Round shot refers to the classic solid spherical cannonball.

Hand culverins

The term "culverin" is derived from the Latin, colubrinus, or "of the nature of a snake". It was originally the name of a medieval ancestor of the musket, used in the 15th and 16th centuries.
The hand culverin consisted in a simple smoothbore tube, closed at one end except for a small hole designed to allow ignition of the gunpowder. The tube was held in place by a wooden piece which could be held under the arm. The tube was loaded with gunpowder and lead bullets. The culverin was fired by inserting a lighted cord into the hole.
These hand culverins soon evolved into heavier portable culverins, around 40 kg in weight, which required a swivel for support and aiming. Such culverins were further equipped with back-loading sabots to facilitate reloading, and were often used on ships.

Field culverins

There were three types of culverin in use, distinguished by their size: the culverin extraordinary, the ordinary, and the least-sized.

The culverin extraordinary had a diameter of 5½ inches (140 mm), a length of 32 calibers (14 ft 8 in; 4.5 m), and a weight of 4800 pounds (2200 kg); it carried a shot with a diameter of 5¼ inches (135 mm) and weight of 20 pounds (9.1 kg).

The ordinary culverin had a diameter of 5½ inches (140 mm), a length of 25 calibers (12 ft; 3.6 m), and a weight of 4500 pounds (2000 kg); it carried a ball of 5½ inches (140 mm) and 17 lb 5 oz (7.9 kg).

The culverin of the least size had a diameter of , a length of 29 calibers (12 ft; 3.6 m), and a weight of 4000 pounds (1800 kg); it carried a shot 3¼ inches in diameter, weighting .
There were also smaller versions, including the bastard culverin (4 inches (100 mm), 7 pounds (3.1 kg) shot) and the demi-culverin or culverin-moyen (4½ inches (114 mm), 10 pound (4.5 kg) shot).
Overall, the culverin was a significant advance over the ballista, which was the "light artillery" unit of the previous eras. Since it fired a ball of iron and relied on gunpowder for propulsion, the heavier ball meant a more stable flight and the gunpowder propulsion meant a faster and farther-ranged weapon. A replica culverin extraordinary has achieved a muzzle velocity of 408 m/s, and a range over 450 m using only mimimal elevation.. This velocity and mass imply that the cannonball had a kinetic energy of roughly 600,000 joules when leaving the muzzle.

The culverin was later replaced by the field gun once technology had advanced to the point where cannonballs had become explosive.

"Hurrah! the foes are moving. Hark to the mingled din,

Of fife, and steed, and trump, and drum, and roaring culverin."

:Macaulay, Ivry, 31-32

"In this, my countrymen, be rul'd by me:

Have special care that no man sally forth

Till you shall hear a culverin discharg'd

By him that bears the linstock, kindled thus;

Then issue out and come to rescue me,

For haply I shall be in distress,

Or you releasèd of this servitude."

:Marlowe, The Jew of Malta, Act V