_Colchester_, which is situated on the river Colne, and perhaps not too far from the shore to take some part in the defence of the coast, has been in its time a place of great importance and of formidable strength. Its walls, of which considerable parts remain, are of Roman workmanship, and its castle, built largely of Roman materials, and therefore by some regarded as Roman in date, is almost unquestionably of Norman construction. It must be admitted, however, that the castle presents several features which differentiate it from the normal castles of the Norman period. Originally the walls were furnished with four principal gates, viz.: Head Gate, North Gate, East Gate, and St. Botolph's or South Gate, and three posterns, viz.: West Postern in St. Mary's Street, Schere Gate or South Postern, and Rye Gate or River Postern, but these have been demolished. The north and west sides of the town were defended by strong earthworks. The place was besieged for eleven weeks during the Civil War. It was held by the Royalist party, and on its fall, two of its most gallant defenders, Sir Charles Lucas and Sir George Lisle, were shot under the castle walls. The weakness of mediaeval castles, built merely for passive resistance, has frequently been noticed, and what is true of them is equally true of the mediaeval walled town. Forces shut up within walls are obviously unable to prevent an enemy from over-running a country. It must be borne in mind, however, that the purpose of fortifications behind walls was not, and never has been, merely intended to oppose the ravages of the enemy. In that part of our military history which is subsequent to the use of gunpowder, the uses of walled defence has been varied and manifold. For example: they were intended to check the enemy's advance; to give time for mobilization; to protect the strategical disposition of the army, especially in the early stages of a campaign; to protect important junctions in the lines of communications; and to safeguard magazines and stores against sudden and surprise attack of the enemy. _Cowling._--The castle at Cowling or Cooling, situated about seven miles to the east of Gravesend, and just two from the sea-shore, was built between 1380 and 1385 by John de Cobham. The gatehouse, built in the regular form in vogue during the latter end of the fourteenth century, and comparable with that at Saltwood Castle and the West Gate of Canterbury, still remains in good preservation, as well as a good deal of the walls and angle-towers enclosing the inner ward, and certain parts of the walling enclosing the outer ward. The gatehouse just referred to is on the south side of the outer ward, to which it gives access. [Illustration: FIG. 23. COWLING CASTLE, KENT, 1784]