Again, many barons threw up castles in the centre of, or adjacent to, pre-existing towns, the subsequent fortifications of which became an integral part of the whole scheme of defence, as at Warwick, Nottingham, and Leicester. Wherever a castle was built for the double purpose of overawing a town and defending it against a common enemy, it is generally found placed upon the city defences or immediately adjacent thereto; and as the settlement had invariably originally sprung up in the vicinity of, or upon the banks of, a river, the fort is usually found placed at the junction where the borough and the river defences meet. A fortress situated in this position would be able to afford material help to a relieving army, while at the same time in the event of the town being captured and given to the flames it would occupy the best possible position, short of being entirely outside the walls, for the garrison to escape the effects of the conflagration. This position of the castle with respect to the town walls and other defences will be recognised in the cases of Warwick, Hereford, Stamford, Cambridge, Bedford, Chester, Shrewsbury, etc. [Illustration: KENILWORTH CASTLE, WARWICKSHIRE.] The Motte and Bailey castle was, as a general rule, placed upon the banks of a river, which thus ensured immunity from attack upon one side, while at the same time supplying the water for the ditches defending the other three sides. In many examples, however, the defence depended upon dry ditches. The proximity of high land apparently had no bearing upon the choice of position, unless of course it was dangerously near; it was only upon the introduction of gunpowder that the presence of commanding spots in the neighbourhood became of importance in the selection of a site. We find, however, that the positions usually chosen enabled the garrison to command a view over the surrounding country, and this feature is a prominent one at Richard's Castle, which affords a wide extent over the northern part of Herefordshire. This is also the case at Belvoir, which occupies a similar position with respect to the great plain of Nottinghamshire. There were naturally a number of points which had to be taken into consideration in the selection of a site, but those enumerated were among the most important; one fact is forcibly borne in upon the mind when viewing the positions of these ancient fortresses, namely, that the builders had a keen eye for the recognition of salient points in the ichnography of a district.