_Cissbury_, north of Worthing.--This great fortress was constructed by men of the Flint Age, and indubitable proofs of its occupancy by a permanent population engaged in a staple trade are afforded by the immense remains of flint chippings within its area, the product of many generations of flint-knappers. The deep and wide pits within it were dug for the purpose of obtaining flints, the raw material of their industry, and these excavations were subsequently utilised for dwelling-places. The fort is advantageously situated upon the trading route between the inhabitants of the Great Forest of Anderida, covering the Weald of Sussex, and the maritime population of the southern littoral; and this fact appealed not only to Neolithic man but also the men of the Bronze and Iron Ages, who occupied it in succession. It is a camp of the plateau type with an inner vallum rising nearly 50 feet above the fosse and 20 above the inner area. General Pitt Rivers estimated that 5000 men would be required to man the ramparts effectually. [Illustration: THE BEAUCHAMP TOWER, TOWER OF LONDON.] _Ravensburgh Castle, Hexton, Herts._--The northern escarpment of the Chiltern Hills is marked by numerous deep ravines leading down with winding courses to the lowlands. This has the effect of leaving bold bluffs of chalk standing up between them, and upon one of these this remarkably fine hill fortress is placed. In addition to the two ravines lying at the sides it is still further isolated by a third running at right angles between the others. The castle occupies 16 acres of the western half of this plateau, and possesses double ramparts on three sides and triple on the north. The section AB shows the steep descent into the ravine upon the south side, and DE indicates the same, while clearly showing the three lines of defence formed by the two ditches. The scarps are remarkable for their clean and smooth surfaces, the chalk presenting the appearance of having been cut with a huge knife. The entrances into the defence lie at nearly 500 feet above the sea-level. [Illustration: RAVENSBURGH CASTLE, HEXTON, HERTS.]