towns on the river, and the garrison, as at Nottingham, was formed out of the inhabitants. Some of these _burhs_, as we have seen, were in the occupation of the Northmen; and at a later date, when the frontier of the west Saxon kingdom had been pushed back, and English kings were again placed on the defensive, Lincoln, Nottingham, Derby, Stamford, and Leicester became known as the five _burhs_, the centre of Danish power in the Midlands. There is no reason to suppose that there was any essential difference between the _burhs_ of Danes and Saxons—that the _burh_ which Æthelflæd took at Derby was in any way different from her own _burh_ at Tamworth. When the Danes first landed on a river bank or island and beached their ships, they constructed what is called in the Chronicle a _geweorc_, _i.e._, a thing wrought. This probably consisted of a slight bank and ditch enclosing the landward side of their position. Where they raised permanent dwellings within the _enceinte_, the _burh_ grew out of the _geweorc_, just as a Roman station developed out of a mere camp. However, it is unsafe to push the phraseology of the Chronicle too far, or to fasten a too technical meaning upon its words; and the fact remains that the term _geweorc_ may be very well applied to a wrought _burh_. The Danish _burhs_ at Huntingdon and Tempsford, the landmarks of their progress up the Ouse to recover Bedford in 921, are called indiscriminately _burh_ and _geweorc_. [Illustration: Map of Saxon and Danish Burhs [The line from the Mersey to the Wash roughly indicates the Danish frontier.]]