Based on the Germanic warda, a military term originated in the Low Frankish area, namely *balward. Within the county of Flanders, *balward developed into an institution (better known as balfart) which was responsible for bolwerc, being the construction and maintenance of fortifications. In course of time, bolwerc became a common name for the physical result of these efforts. A terminological confusion between both terms led to the materialization of *balward as *bolward, which gave rise to the French boulevard. Early differentiation of the Low Frankish *balward resulted in two variants for 'belfort', namely *balferd and balfred. The first variant independently developed in Flanders and was introduced in the French-speaking area. The second variant, conserved in Medieval Latin, spread from the Low Frankish region to the English-speaking area. The remarkable German spelling bergfried can be explained by south-east migration of the hybrid form *balgfred.