394 THE POPULAR SCIENCE MONTHLY. 



In considering the economical side, account must be taken of the 

 density of the population and the frequency of communications. It 

 is important that the principal centers be connected by wide, direct, 

 and easy roads following the course of the most usual commercial cur- 

 rents. Theoretically, the width of each street should be proportionate 

 to the traffic upon it. 



Historical considerations may sometimes rule, for due force must 

 be allowed to existing conditions in the construction of each new 

 street. 



Sometimes cities are built so fast that we might say they are made 

 up of sections constructed after a plan framed in advance. In such 

 cases they generally present a regular disposition. Such a town is 

 Carlsruhe, in Baden, where the avenues converge toward the Chateau, 

 and of such character are most American cities. Generally, however, 

 in old Europe, cities develop themselves slowly, and the laying out of 

 their streets has been influenced by the circumstances in their history. 



Open cities generally expand gradually by the building of houses 

 along the roads toward neighboring towns. They thus take a kind of 

 radiated or palmate form, quite favorable to facility of communication. 



Fortified cities are developed in an intermittent way. After hav- 

 ing been for a long time smothered within their walls, they end by 

 breaking the barriers down and uniting with their suburbs ; construct- 

 ing elegant boulevards in the places formerly occupied by their forti- 

 fications. The city of Paris bears the marks of several changes of this 

 kind. Generally the extension takes place alike in all directions, and 

 the towns that have undergone such metamorphoses present a succes- 

 sion of concentric zones separated by circular boulevards. The cen- 

 tral nucleus generally offers a close agglomeration of high houses part- 

 ed by narrow, crooked, and everywhere crowded streets. Here public 

 and private business is transacted, and the centers of trade and amuse- 

 ment, the public offices, and the churches, are established. Through 

 this part also lie the usual ways of passage from one suburb to another. 

 Most frequently the old town is traversed by a grand artery, the history 

 of which goes back to the origin of the place, and which is usually 

 busy with trade and much crowded. The population of the suburbs 

 is generally less dense than that of the city proper ; and the streets are 

 wider, and the houses farther apart. The inhabitants of the suburbs 

 are in the habit of going frequently to the center of the city, because 

 it is the most populous part, and because the roads to the other suburbs 

 lie through it. The principal streets of the suburbs also converge 

 toward the center. 



All the characteristics we have sketched may be found in the city 

 of Vienna, where the ancient city, still called die Stadt " the City," 

 rests on a branch of the Danube in the north, and on the Wien in the 

 southwest. The cathedral, situated in the center of the town, St. Ste- 

 phen's Place, and the Graben, are still the points toward which the 



