Burhs also had a secondary role as commercial and sometimes administrative centres. Their fortifications were used to protect England's various royal mints.
Burh and burg were Old English developments of the Proto-Germanic word reconstructed as *burg-s, cognate with the verb *berg-an ("to shut in for protection"). They are cognate with German Burg and Scandinavian borg and, in English, developed variously as "borough", "burg", and (particularly in the East Anglian region of England and Scotland) "burgh".
Byrig was the plural form of burh and burg: "forts", "fortifications". It was also the dative case: "to the fort" or "for the fort". This developed into "bury" and "berry", which were used to describe manor houses, large farms, or settlements beside the fortifications.
In addition to the English foundations described here, these names were sometimes used in Old English calques or variants of native placenames, including the Brittonic *-dunon and Welsh caer, as at Salisbury.
Burhs were originally built as military defences. According to H. R. Loyn, the burh "represented only a stage, though a vitally important one, in the evolution of the medieval English borough and of the medieval town". The boundaries of ancient burhs can often still be traced to modern urban borough limits. Most of these were founded by Alfred the Great in a consciously planned policy that was continued under his son Edward the Elder and his daughter, Æthelflæd, the 'Lady of the Mercians', and her husband Æthelred, Ealdorman of Mercia. The Mercian Register tells of the building of ten burhs by Æthelflæd, some as important as Tamworth and Stafford, others now unidentifiable.