While besieging a fortified place, in the early Middle Ages, German soldiery sometimes protected themselves under the shelter of a movable wooden tower.
This protection they called a bergfrid, literally, shelter shed.
The device was soon borrowed by the armies of other countries, and the soldiers probably thought that they were still using its German name. But by the time it reached England, in the early fourteenth century, the name was spoken and written berfrey.
Within another hundred years this had become belfroy and belfrey, winding up as belfry. The name resulted from mispronunciation, for there was then no association with bells.
Along with altered name, the structure began to acquire a different military use and to become a formidable mechanism of offense.
It was made of sufficient height to enable archers, sheltered by its roof, to overlook the fortified place under siege and fire directly at persons within. But when gunpowder replaced arrows, these cumbersome wooden, towers were no longer of use in military operations.
Probably at first, then, because there was no other use for them, it was found that they did serve as excellent watchtowers, when hauled within the walls of a city. A watchman stationed within could sound an alarm upon the approach of danger. For such purposes these towers were then provided with bells.
Ultimately, as we know, the towers were attached to church buildings, sometimes erected to great heights; the bells, except at rare times of great public peril or celebration, serve only to summon the populace to worship or to announce the passing time.