In the Middle Ages their functions were perfectly distinct. The architect constructed what the _engigneur_ used his utmost cunning to destroy. The architect built ramparts and strengthened them with towers; the _engigneur_ undermined them if attacking, or countermined them if defending. It was his business to invent or direct the use of engines of war, such as rams, mangonels, arblasts, and machines for the slinging of enormous projectiles, or grenades. He constructed the portable wooden towers which the besieging party brought up against the walls for an escalade, directed the sappers who undermined them, and, in fact, superintended the manufacture of all such offensive engines as were necessary in the conduct of a siege, a process which, before the invention of firearms, necessitated preparations as prolonged and tedious as they were complicated and uncertain. In short, the architect was the constructor of fortifications, the _engigneur_ their assailant or defender. It was not until the time of Vauban that military engineers were called upon to exercise functions so much more extensive. At an earlier period there were, however, specialists in construction who undertook such works as the circumvallation of Aigues-Mortes, but their labours had little in common with those of modern engineers. [Illustration: 164. CITY OF CARCASSONNE. RAMPARTS TO THE SOUTH-EAST] Before the feudal period the fortifications of camps consisted either of earthworks, of walls built of mud and logs, or of palisades surrounded by ditches, in imitation of the Roman methods of castrametation. The _enceintes_ of towns fortified by the Romans were walls defended by round or square towers. These walls were built double; a space of several yards intervened, which was filled up with the earth dug from the moat or ditch, mixed with rubble. The mass was levelled at the top and paved to form what is technically known as a covered way, or terrace protected by an embattled wall rising from the outer curtain. That portion of the _enceinte_ of Carcassonne which was built by the Visigoths in the sixth century is thus constructed on the Roman model. "The ground on which the town is built rises considerably above that beyond the walls, and is almost on a level with the rampart. The curtains[58] are of great thickness; they are composed of two facings of dressed stones cut into small cubes, which alternate with courses of bricks; the intervening space is filled not with earth, but with a concrete formed of rubble and lime."[59] The flanking towers which rise considerably above the curtains were so disposed that it was possible to isolate them from the walls by raising drawbridges. Thus each tower formed an independent stronghold against assailants. [58] The wall space between the towers. [59] Viollet-le-Duc, _La Cité de Carcassonne_.