These were (1) the division of the fyrd or national militia into two parts, relieving each other at fixed intervals, so as to ensure continuity in military operations; (2) the establishment of fortified posts (burgs) and garrisons at certain points; (3) the enforcement of the obligations of thanehood on all owners of five hides of land, thus giving the king a nucleus of highly equipped troops.
The German name is usually derived from the seven principal fortified towns or burgs," founded by the German colonists, though some authorities prefer to connect it with the Cibin Mountains on the south frontier.
Normandy was the best-governed part of France in the nth century; and the Danes in East Anglia and the Five Burgs were in many regards a model to their Saxon neighbours (Steenstrup, op. cit.
Its name is derived from Ath-na-riogh, the ford of kings; and it grew to importance after the AngloNorman invasion as the first town of the Burgs and Berminghams. The walls were erected in 1211 and the castle in 1238, and the remains of both are noteworthy.
This special legal status probably arose from the towns being considered in the first place as the king's fortresses 3 or burgs (see Borough), and, therefore, as participating in the special peace enjoyed by the king's palace.