Jacob Riis worked as a police reporter for the New York Tribune after immigrating to the United States in 1870. Throughout the late 19th century, a large part of his work uncovered the lifestyle of the city’s tenement slums.

Here, an Italian immigrant rag-picker is seen with her baby in a small run-down tenement room on Jersey Street in New York City in 1887. During the 19th century, immigration doubled the city’s population every year from 1800 to 1880.

Houses that were once for a single family were often divided up to pack in as many people as possible, as this 1905 photo shows.

A young girl, holding a baby, sits in a doorway next to a garbage can, in New York City in 1890. Tenement buildings often used cheap materials, had little or no indoor plumbing nor proper ventilation.

Immigration provided a large pool of child laborers to exploit. This twelve-year-old boy, shown in this 1889 photo, worked as a thread-puller in a New York clothing factory.

A shelter for immigrants in a Bayard Street tenement, shown in 1888. To keep up with the population increase, tenements were constructed hastily and often without regulations.

Three young children huddle together for warmth above a grate off of Mulberry Street in New York, 1895. Housing was not only constantly divided up within buildings, but also began to spread to backyards in an effort to use every inch of space in poor areas.

This man sorts through trash in a makeshift home under a dump on New York City’s 47th Street. In 1890, Riis compiled his work into his own book, titled How the Other Half Lives, to expose the brutal living conditions in the most densely populated city in America.

His book caught the attention of then-Police Commissioner Theodore Roosevelt. This photo shows a man’s living quarters in the cellar of a New York City tenement house in 1891.

By 1900, more than 80,000 tenements had been built in New York City and housed 2.3 million people, or two-thirds of the total city population. This peddler sits on his bedroll, atop two barrels, in his cellar home.