This was at a time when there was much discussion in France about the breakup, even disappearance, of the traditional family unit. Much was blamed on railroads, which, it was felt, made people too mobile.

Zola resolved to write two novels a year for the next twenty years, all about the fictional Rougon-Macquart family from Provence. He more or less kept to that schedule, occasionally frustrated, such as when Germinal, the miners' saga that many consider to be his masterpiece, took an entire nine months. By 1869, he had the cycle mapped out, and between 1872, at the age of thirty-two, and 1892, at the age of fifty-three, he carried out this plan. Zola had the words Nulla dies sine linea, “No day without a sentence,” engraved over his desk, but in truth he produced considerably more than a sentence. On most days he produced four handwritten pages, sometimes stopping the day's work in midsentence. He titled the series The Rougon-Macquarts: The Natural and Social History of a Family under the Second Empire. By its completion in 1892, the cycle consisted of twenty novels in thirty-one volumes and included all of the novels that have been deemed his most important work. He had created twelve hundred characters. He produced the first six books in five years. The Belly of Paris was the third.

When they were young his painter friend Paul Cézanne started to have doubts about his future, and Zola, trying to encourage him, wrote, “There are two men in an artist, the poet and the worker. He is born a poet, and he becomes a worker.”

He began his undertaking with a sense of inadequacy, believing that he had neither the depth of Balzac nor the poetic ear of Hugo. Zola wrote in a simple language, with great power but occasional clumsiness, even bad usage, which might be explained by the speed at which he worked. One of the great challenges of translating Zola is resisting the occasional desire to improve him. He needed more editing, and the translator has to resist providing it.

Zola's portrayals of poverty were shocking to readers of the time, especially the lower classes, who did not want to be seen that way. Readers were accustomed to having a certain degree of romance overlaid on misery. His raw portraits of the have-nots made his haves look all the more guilty. There is no poetry in Zola's novels. They are unflinchingly realistic, and this was a source of his power. Eventually it was the work of Zola more than other great writers that stirred the conscience of the middle class.

He had a close circle of friends with whom he frequently lunched, which included other writers such as Gustave Flaubert, Edmond de Goncourt, and Alphonse Daudet. In this circle Zola was known as someone who loved food, ate well and bountifully, and spoke very little unless fired up about some issue or when asked a question about his work. He seems to have been a shy man until sparked by one of his many passions. Some in this group, such as Flaubert, also mingled with members of the upper class, a social milieu in which Zola had no experience. From them he would extract knowledge for portraying those characters. It was one of a number of tricks Zola copied from Balzac.

All of the writers and artists of his group called themselves “naturalists,” a term coined by the painter Gustave Courbet. Zola pointed out that the term had a long history. In the seventeenth century, it had been used in philosophy to mean a school of thought that held up nature as the model. Naturalists, then, were predominantly atheists. After the emergence in the mid-nineteenth century of Darwin, whose principal works were published when Zola was a student, the term “naturalists” described those who used scientific methods. According to Zola, a naturalist artist used scientific methodology but infused it with his own language and personality.