With the social changes among the invaders changed also the character of their military, or rather of their mixed military and domestic, works. The British encampments, intended for the residence of a tribe having all things in common, were, both in position and arrangements, utterly unsuited to the new inhabitants. The Roman stations, intended for garrisons, save where they formed part of an existing city, were scarcely less so, nor were the earlier works of the Northmen suited to their later wants. These were mostly of a hasty character, thrown up to cover a landing or to hold at bay a superior force. No sooner had the strangers gained a permanent footing in a district than their operations assumed a different character. Their ideas were not, like those of the Romans, of an imperial character; they laid out no great lines of road, took at first no precautions for the general defence or administration of the country. Self-government prevailed. Each family held and gave name to its special allotment. This is the key to the plan of the later and great majority of purely English earthworks. They were not intended for the defence of a tribe or territory, nor for the accommodation of fighting men, but for the centre and defence of a private estate, for the accommodation of the lord and his household, for the protection of his tenants generally, should they be attacked, and for the safe housing, in time of war, of their flocks and herds. These works, thrown up in England in the ninth and tenth centuries, are seldom, if ever, rectangular, nor are they governed to any great extent by the character of the ground. First was cast up a truncated cone of earth, standing at its natural slope, from twelve to even fifty or sixty feet in height. This “mound,” “motte,” or “burh,” the “Mota” of our records, was formed from the contents of a broad and deep circumscribing ditch. This ditch, proper to the mound, is now sometimes wholly or partially filled up, but it seems always to have been present, being in fact the parent of the mound. Berkhampstead is a fine example of such a mound, with the original ditch. At Caerleon, Tickhill, and Lincoln it has been in part filled up; at Cardiff it was wholly so, but has recently been most carefully cleared out, and its original depth and breadth are seen to have been very formidable. Though usually artificial, these mounds are not always so. Durham, Launceston, Montacute, Dunster, Restormel, Nant cribba, are natural hills; Windsor, Tickhill, Lewes, Norwich, Ely, and the Devizes, are partly so; at Sherborne and Hedingham the mound is a natural platform, scarped by art; at Tutbury, Pontefract and Bramber, where the natural platform was also large, it has been scarped, and a mound thrown up upon it.