The Romans, who always had a keen eye for favourable defensive sites, were scarcely likely to miss the high ground in the great bend of the Medway not far from where it falls into the Thames. The Watling Street from Dover to London passed the river, moreover, at this point and received protection from the Roman camp. The Saxons and Danes also maintained the Castle of Hrofa here. The usual timber fortifications were constructed in an oblong enclosure of about seven acres, including a large conical mound of the Eastern chalk range called Bully Hill. It must even at that date have been a place of some strength, because when it was besieged by the Danes in 885, it was able to hold out long enough for Alfred to come to its relief. At the Conquest, the Normans recognized the strength of the position and added their own improved methods of fortification, enclosing a quadrangular space close to the river with a strong curtain wall and afterwards building a massive square keep in the enclosure. The Saxon works were left outside and used merely as an outpost, as was the case at Warwick and Canterbury. The original quadrangular enclosure had a wall-circuit of 580 yards, the North and South walls measuring 160, and the East and West 130 each. The East front faced the cathedral which even at that day was venerable. The West wall ran along the river front. The other three walls were defended by a broad and deep moat, traces of which still remain. Much of the outer wall, with square open towers recurring at intervals also exists. The main entrance or gatehouse with drawbridge, which no longer exists, was at the North-east angle, from which there was a steep descent to what is now the High Street. At the North-west angle, was a bastion tower with a postern gate. Although this tower no longer exists, it was still standing as late as 1735, immediately on the shore, commanding the bridge. A large round tower still stands at the South-east angle. It measures thirty feet in diameter; it has two floors and is loop-holed for archery. Two rectangular towers that defended the East front are still in existence. Throughout the constructions, we cannot fail to notice and admire the strength and massiveness of the masonry. To this the ruin owes its preservation, for besides the destroying hand of time, the neglect of unappreciative generations, and the destruction wrought by greed and fanaticism, it has also suffered from several sieges.