The main gate of the ramparts, which was built between 1415 and 1420, is to the west of the place, in the curtain flanked by the tower known as the Tour du Roi. This gate and the lateral postern gave access to the town, their drawbridges forming a passage across the moat when lowered, and when raised, an initial barrier to assailants. Above the gates was the warder's lodging, beneath which the vaulted passage and the postern communicated directly with an outer guard-room in the ground-floor of the Tour du Roi. In addition to the first barrier, formed by the raised platform of the drawbridge, the main entrance was secured by double doors, and by an iron portcullis, which still remains in its lateral grooves. The great arch is crowned by a tympanum, on which the united arms of the king, the abbey, and the town were carved.
The works designed for the defence of rivers flowing through fortified towns, or of the inlets of harbours, are closely allied to the military architecture of gates. At Troyes the river arches in the town ramparts were guarded by gratings or portcullises of iron. At Paris the passage of the Seine was barred by chains stretched across the river from wall to wall, and upheld in the middle of the stream by piles or firmly anchored boats. At Angers the walls of the town abutted on two towers known as the Haute Chaîne and the Basse Chaîne (the Higher and Lower Chains), containing windlasses for the chains, which at night were stretched across the Maine at its passage through the enceinte.
Seaports were defended at the mouth by towers on either shore, between which chains, worked from within, could be stretched to bar the passage. The harbour of La Rochelle is thus protected. According to some archæologists of authority, the tower known as the Tour de la Chaîne (to the left of the drawing) is older than that of St. Nicholas (on the right), which is supposed by them to have been built in the sixteenth century on the foundations of an earlier tower contemporary with that on the other side of the Channel. The piles upon which these towers stand seem to have given way in part, and to have caused a perceptible inclination of the Tower of St. Nicholas.
194. ENTRANCE TO THE PORT OF LA ROCHELLE. TOWER OF ST. NICHOLAS, AND TOWER CALLED TOUR DE LA CHAÎNE. BEFORE THE RESTORATION
The suggestion made in a very fanciful modern design, that the two towers were once united by a great arch, is wholly without foundation. Such a useless structure would have entailed defensive works equally useless, seeing that a chain stretched from tower to tower at high tide—at low tide the harbour was inaccessible—would have been perfectly effectual against any vessels of that period attempting to force a passage.
Bridges.—As is the case with all other architectural buildings, the origin of bridges dates back to the Romans, by whom they were often decorated with triumphal arches. The bridge of St. Chamas in Provence, known as the Pont Flavien (Flavian Bridge), is an example which seems to date from the first centuries of the Christian era.
The triumphal arches were in later times replaced by fortifications; they became têtes de pont, bastilles, or crenellated gate-houses, the function of which was not, like that of the arches, the decoration of the structure or the glorification of its founder, but the defence of the passage across the river, and the protection of the fortress with which it communicated.
195. BRIDGE AT AVIGNON. RUINS OF THE BRIDGE KNOWN AS THE PONT DE ST. BÉNÉZET