From earliest times, two motives have governed the location of cities: either the site was selected because it offered natural means of defense, or else commerce gathered men at a particular point, about which they built fortifications. In either case, the necessity of protection against enemies from without conditioned the form and arrangement of the city. Even in this western hemisphere the question of defense has been of moment. Louisburg and Quebec; Boston, New York, and Yorktown; Mackinac and New Orleans; Charleston, Mobile, Vicksburg, and New Orleans again,—are names which recall sieges and battles of three wars; while the walled towns of Europe find their counterparts in the palisaded settlements which sprang up in the Indian country of North America, Chicago itself being a typical example. It is only within recent times that the city has been able to extend its borders free from the restraints imposed by the necessity of warding off a foe. [Illustration: X. THE ACROPOLIS AT ATHENS. From a water-color by E. H. Bennett.] The first city-builder whose exploits are recorded was Semiramis, queen of Babylon; and although the history of that country, as recorded on its monuments, fails to mention even the name of this war-like ruler, we may not disregard the circumstantial accounts given by classical writers of the greatest commercial city of ancient times. Diodorus tells us that Semiramis, being of an aspiring spirit and anxious to excel all her predecessors in glorious actions, set about building a great city in the province of Babylon. First she had complete plans prepared by her architects and artists, then she assembled from all parts of her empire the men necessary for the work of construction. For the promotion of commerce, she located the city on the banks of the river Euphrates; and round about it she built a wall, very high, fortified with many turrets, and so broad at the top that thereon chariots might be driven abreast. Across the river she threw a bridge five furlongs in length, with arches having a span of twelve feet. Along either shore of the river she raised a bank as broad as the wall; and temporarily turning aside the course of the stream, she made in the bed of the river a passage in the form of a tunnel to serve as a connection between her two palaces, which were also lookouts whence she could command every portion of the city. Other cities on the banks of the Tigris and the Euphrates Semiramis built, and there she established traffic centers for the vending of merchandise brought from Media, Persia, India, Egypt, and other countries reached by the two great rivers, which in those ancient times vied with the Nile and the Ganges. So by her able policy she greatly enriched the merchants who trafficked in those parts, and advanced the glory and majesty of Babylon. [Illustration: XI. THE GREEK THEATRE AT SYRACUSE, SICILY. From a water-color by E. H. Bennett.]