The first half of the nineteenth century saw the arrival of many thousand immigrants from Europe. These, with the thousands of people who came from other parts of America, attracted by the city's growing industries, made more and more room necessary. First, about 13,000 acres across the Harlem River were added to the city. Then, in 1895, the city limits were extended to the borders of Yonkers and Mt. Vernon. And finally, in 1898, New York, Brooklyn, Long Island City, and some other near-by towns were united under one government, forming together Greater New York, the largest American city and the second largest city in the world. New York to-day covers about 360 square miles, its greatest length from north to south being 32 miles, its greatest width about 16. The city is divided into five boroughs: Manhattan, The Bronx, Brooklyn, Queens, and Richmond. The Borough of Manhattan, on the long narrow island of that name, lies between the Hudson and the East River. North and east of Manhattan, on the mainland, lies the Borough of The Bronx. Just across the narrow East River, on Long Island, are the boroughs of Queens and Brooklyn; while Staten Island is known as the Borough of Richmond. [Illustration: NEW YORK SKYSCRAPERS] As more and more people came to the city the business area on Manhattan proved too small, and with water to the east, to the west, and to the south, there was no possibility of spreading out in these directions. Yet business kept increasing, and the cry for added room became more and more urgent. Finally, the building of the ten-story Tower Building in 1889 solved the difficulty. It showed that, though hemmed in on all sides, there was still one direction in which the business section could grow--upwards. And upwards it has grown. To-day lower Manhattan fairly bristles with huge steel-framed skyscrapers which furnish miles and miles of office space, twenty, thirty, forty, in one case even fifty-five, stories above the street level. The supplying of office and factory space is not the only use that has been made of these steel buildings. Great apartment houses from twelve to fifteen stories high provide homes for thousands. Mammoth hotels covering entire city blocks furnish temporary homes for the multitudes which visit the city each year. Fifteen of the largest of these can house more than 15,000 guests at one time--a good-sized city in itself. Thus has Manhattan become one of the most densely populated areas on the globe. In the boroughs of Queens and Richmond, on the other hand, large tracts of land are given over to farms and market gardens. [Illustration: HOW A SKYSCRAPER IS MADE] Manhattan is at once the smallest and the most important borough in the city. Here are the homes of more than 2,000,000 people, the business section of Greater New York, and the chief shipping districts. [Illustration: A MAMMOTH HOTEL]