‘Every great city has one or more slums, where the working-class is crowded together. True, poverty often dwells in hidden alleys close to the palaces of the rich; but, in general, a separate territory has been assigned to it, where, removed from the sight of the happier classes, it may struggle along as it can. These slums are pretty equally arranged in all the great towns of England, the worst houses in the worst quarters of the towns; usually one- or two-storied cottages in long rows, perhaps with cellars used as dwellings, almost always irregularly built. These houses of three or four rooms and a kitchens form, throughout England, some parts of London excepted, the general dwellings of the working-class.’
Frederick Engels, The Condition of the Working Class in England, Leipzig, 1845 (translated in English 1883