At the first invasion of Caesar, 55 B.C., we read of no towns being assaulted, but in the next, 54 B.C., the great _oppidum_ of Cassivelaunus was taken by storm after the passage of the Thames. This capital, Verulamium (adjacent to the modern St. Albans), was a large oval enclosure defended upon three sides by a deep fosse and vallum, in one place doubled, and upon the other by an impassable marsh. The city was attacked in two places and captured. In A.D. 43 the final subjugation of England took place, and the vallum at Verulamium was crowned by the Romans with a massive wall of masonry, great portions of which still remain, supplanting the former wooden obstructions. That which occurred at Verulamium happened also in numerous other places, Silchester for example, the Romans thus adapting an efficient earthwork to suit their own requirements. Where, however, pre-existing works did not occur, the walls, ramparts, and fosses were invariably constructed round a rectangular area such as may be seen at Chester. The enclosed streets crossed each other at right angles, and this feature is a marked one in Verulamium, although, as stated, the defences do not conform to the rectangular shape. Isolated earthworks constructed during the Roman Period are always more or less square. [Illustration: MELANDRA, DERBYSHIRE.] _Melandra_ is a Roman earthwork in a good state of preservation near Glossop in Derbyshire. It is almost square, and consists of a simple vallum and external fosse. There are four openings caused by two main roads which intersected at the centre of the earthwork. It affords an example of the prevailing structure of Roman Camps, which are numerous in those parts of the British Isles which owned the sway of the conquerors. The many camps, for example, upon the Watling Street all exhibit the same general plan, based upon the formation of the Roman legion.