Pharos or lighthouses, intended as sailing-marks for guiding ships into porta opposed to warnings against dangerous coastal features, were in un among the ancients from the Hellenistic period onwards; the famous Pharos of Alexandria was built in the third century B.C. Such lighthouses are shown in antiquity as surmounted by virtual open bonfires or beacons. But another type, crowned by a roofed lantern-tower, is shown upon Trajan's Column.
Only two Roman lighthouses are known in Britain, one on each side of the harbour at Dover, which was reached by setting a course exactly between them. That on the east side, on Castle Hill, is still standing to a height of 62 feet, of which 48 feet are Roman work, the rest, together with most of the external face, being medieval. It is octagonal in plan externally, each side 15 feet long at the base; internally it is 15 feet 10 inches square. The sides rose vertically and were stepped back at each storey, while the known dimensions suggest an original height of about so feet; for at that height the walls, 12 feet thick at the bottom, would have been diminished by the successive offsets to between 3 and 4 feet. The core of the walls is a fine rubble aggregate, grouted with lime mortar, the faces ashlar, and at every seven courses there is a bonding-course of tile. The doorway, and the recesses and windows which occur at each storey, are mostly arched with tufa voussoirs alternating with pairs of tiles. Each storey had a wooden floor, the first floor being 174 feet above ground, the others at intervals of 7 to 8 feet. In the main, this tower must have resembled the vanished Tour d'Ordre, the Roman lighthouse at Boulogne, which was also octagonal in plan and of similar profile, but was 200 feet high.
The second lighthouse at Dover, on the Western Heights, is now represented only by a mass of masonry, traditionally known as the Devil's Drop' on account of its lumpish shape and the hardness of its mortar, embedded in the 'Drop Redoubt'. Of the tower's original plan and dimensions nothing definite is known, but its foundations, seen when the redoubt was being built in 1861, appear to have been constructed. at least in part, of re-used materials, as if erected late in the Roman period.