Les Rougon-Macquart is a twenty book cycle by French author Émile Zola which follows both the legitimate and illegimate branch of a fictional family living during the Second French Empire (1850-1870). Written in a Naturalist style, each book takes a deep dive into different areas of life during this time period, from trains, prostitution and politics to mining, agriculture and religion. Books are listed in publication order, but only loosely follow each other. Don't know where to start? See this post for why you don't have to start with book 1, and this post for the main themes of each book. 

(Note for English readers: If possible, try to seek out modern translations. Early translators were often forced to leave out content due to censorship)