Byzantium.—The ancient Greek city, Byzan tium, was built on a site that was strategically excellent, surrounded, as it was, by water on three sides and protected from the ravages of the barbarians by a wall on the north side. The traditions relating to the construction of the walls cover all the discoveries and technique of the various ages of Greek and early Roman civilization. The Byzantine walls of mediaeval Constantinople consist of three distinct sections: that on the west toward landward side; sec ondly, that on the Golden Horn; and third, that on the Marmora or the seaward side. The Byzantine city was completely enclosed by these wall sections. In the design of all of the By zantine fortification construction, aesthetic pos sibilities have been suppressed and completely subordinated to the requirements of defense.
The widespread influence of Constantinople carried the spirit of the Byzantine science of military engineering throughout Mesopotamia, Asia-Minor, northern Africa and southern Spain. At Granada, in Spain, the 101 domi nating the city was crowned with the strongly fortified palace of the ruler. The enclosure was surrounded by a strongly-built wall, rein forced by great defensive towers that served to render the palace, in its day, practically im pregnable.
Middle traditions of Rome, with here and there modifications due to Byzantine influence, determined the arrangement of the defenses of the fortified towns and castles of the Middle Ages. The cities were often pro tected by several walls; at other times the city proper was located upon the highest available ground and surrounded by heavy walls. Its suburbs were outposts, furnished with protec tive towers and curtain walls. From the 3d to the 11 th centuries the Roman defensive sys tem underwent but little modification. The most notable existing example of this period is the reconstructed Visigothic city of Carcas sonne. This was a frontier city of the greatest importance. During the 13th century the Visi gothic enceinte was thoroughly repaired and the celebrated Tresan tower and Narbonnaise gate on the eastern side were erected. The castle is the most carefully defended work of the period and the precautions taken to ensure its safety arouse the admiration of all who study its intricate arrangement of moats, ramparts and barbicans, or advance fortified towers. Ra gusa, on the eastern shores of the Adriatic, and Haidra, Africa, serve to visualize for us the massive picturesque security that made these cities practically unconquerable previous to the use of artillery. In Italy the great feudal lords, commanding lofty sites in the neighborhood of cities, erected secure fortresses. During the first half of the 12th century, due to the in tolerable depredations of the half-savage nobles, the various cities of northern Italy overcame and dispossessed the majority of the feudal chieftains and forced them to come into the cities. The great residences that they built were
provided with high and strongly-fortified tow ers. These constructions made it possible for the nobles to defy the municipal restrictions and set at naught the conventions of the city. The famous leaning towers of Bologna, the Asineni and Garisenda (12th century) are among the very few remaining examples of the Italian defensive towns of the Middle Ages.
The castles serving as a refuge for a town garrison differed in general plan from the castles of the isolated nobles, which aimed to procure the security that was so well obtained in the Chateau-Gaillard, built by Rich ard Caur-de-Lion in the Andelys. Selecting a place where a sharp bend in the Seine formed a st 'ategically strong peninsula, and this penin sua being made secure, on a lofty promontory on he opposite bank the major fortress was buil• To the south a tongue of rock, less than 15 ;r1 width, served to connect the isolated promontory with the adjacent hills. This was the only attackable point of the fortress. To protect this vulnerable point a strong tower flanked by subordinate ones and curtain walls was built and so commanded the plateau. This outwork was separated from the enceinte o: the castle by a deep ditch excavated in the rock. The body of the place consisted of two parts, the lower court, and, separated from this by a moat, the internal castle, with its elliptical enceinte. The strength of the defense culmi nates in the keep or donjon. The donjon was to the castle what the castle was to the for tified towns— its last retreat, and upon it there fore was lavished the utmost care.
Artillery — Modern.-- Toward the middle of the 15th century artillery had attained a great development. As a result of this progress the problems of attack and defense were wholly changed. In attack, how strangely modern reads this excerpt from the 'Past and Future of Artillery,) by L. Napoleon Bonaparte, Vol. II: of erecting bastiles all round the town, the besiegers established before the great fortresses a park surrounded by an intrench merit, beyond the reach of cannon. From this point they conducted one or two branches of the trenches towards the point where they estab lished their batteries. . . . We have arrived at the moment when trenches were employed as a means of approach concurrently with covered ways of timber.° It was obligatory, in view of the new agencies of war, to replace the picturesque high, machicolated towers and battlemented walls of feudalism with low breastworks on an extended line. The per sistency of tradition, however, caused the re tention in numerous places of feudal forms until well in the 17th century.