Fire is communicated to the combustible matter within the shell by means of a fuse, which is so regulated that the explosion shall take place at the desired moment.

Hollow-shot are used with advantage to destroy ordinary buildings, ships, earthwork, and thin walls of masonry; they, however, are of little avail in breaking the massive walls of well-constructed forts.

Howitzes and grenades are particularly effective against cavalry and columns of infantry, and are much employed on the battle-field; they are also much used in the attack and defence of places.
We find that as early as 1486 the Spaniards made use of a projectile similar to the modern bomb.

"They threw from their engines large globular masses, composed of certain inflammable ingredients mixed with gunpowder, which, scattering long trains of light," says an eye-witness, "in their passage through the air, filled the beholders with dismay, and descending on the roofs of edifices, frequently occasioned extensive conflagration." In the siege of Constantinople by Mahomet II., shells were used, and also mortars of enormous size.

In 1572 Valturus proposed to throw, with a kind of mortar, "globes of copper filled with powder." In 1588, an artificer of Venloo burned Wachtendeck by throwing bombs into the place.