The constructive methods employed in the building of fortified gates were modified as military architecture progressed on lines already considered by us in the first chapter of this section, when dealing with defensive methods generally, which, in the fourteenth century, seem to have been in advance of those of attack. A steady improvement in details went on until the invention of gunpowder came in to profoundly modify the conditions alike of defence and assault. [Illustration: 189. RAMPARTS OF AIGUES-MORTES. GATE KNOWN AS THE _PORTE DE LA GARDETTE_. DRAWBRIDGE. (TO THE RIGHT OF THE DRAWING THE _TOUR CONSTANCE_, BUILT BY ST. LOUIS)] The gateways of fortified _enceintes_ were modified in the fourteenth century not only by alterations in the plan of towers, the substitution of stone machicolations for the wooden _hourds_ or scaffoldings of parapets, the addition of portcullises, folding-doors, and the _machicoulis_ of the vaulted passage, but further by the invention of the drawbridge. A drawbridge, it may be hardly necessary to say, consisted of a wooden platform suspended by chains to cross-beams poised on uprights on the principle of a see-saw; when lowered, the bridge afforded a passage across the moat. It was raised by depressing the inner ends of the lever-beams which pivoted upon a fulcrum, and thus brought the platform up vertically against the front of the building, where it formed an outer door which an attacking party had either to batter in or to bring down by cutting the chains. [Illustration: 190. RAMPARTS OF DINAN. GATE KNOWN AS THE _PORTE DE JERZUAL_] It will be readily perceived that such a bridge was infinitely more effectual and more to be depended upon than the portable bridge mentioned in our description of the castle gate of Carcassonne. The latter had to be raised piece by piece, a prolonged operation impossible of execution in case of a sudden surprise. Aigues-Mortes seems to have been one of the first fortresses to which the new methods were applied. The gates east, west, and south are constructed on the twelfth-century system, as exemplified at Carcassonne. But the northern gate, known as the _Porte de la Gardette_, which was either made or altered in the fourteenth century, still shows the grooves for the beams of the drawbridge, and the pointed arch of the doorway is enframed by a square rebate destined for the platform when raised.