A burh () or burg was an Anglo-Saxon fortification or fortified settlement. In the 9th century, raids and invasions by Vikings prompted Alfred the Great to develop a network of burhs and roads to use against such attackers. Some were new constructions; others were situated at the site of Iron Age hillforts or Roman forts and employed materials from the original fortifications. As at Lundenburh (medieval London), many were also situated on rivers: this facilitated internal lines of supply while aiming to restrict access to the interior of the kingdom for attackers in shallow-draught vessels such as longships. Burhs also had a secondary role as commercial and sometimes administrative centres. Their fortifications were used to protect England's various royal mints. Name and were Old English developments of the Proto-Germanic word reconstructed as , cognate with the verb ("to shut in for protection"). They are cognate with German , Dutch and Scandinavian and, in English, developed variously as "borough", "burg", and (particularly in the East Anglian region of England and Scotland) "burgh". was the plural form of and : "forts", "fortifications". It was also the dative form: "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 and Welsh , as at Salisbury. Background 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. Some were based upon pre-existing Roman structures, some newly built, though others may have been built at a later date. Æthelstan granted these burhs the right to mint coinage and in the tenth and eleventh centuries the firm rule was that no coin