If mobility in space is a démographie phenomenon still little known for the XIXth century, this is all the more true as concerns migration within the same town. Yet the phenomenon is important is important both in numbers and so as to be able to account for spatial segregation and social mobility within urban populations. In this paper, we have followed the movements of a thousand new immigrants coming from the country between 1867 and 1872 in the town of Châtelent and the industrial area of Charleroi. First, where do the immigrants go when they arrive in the town ? By carving up the town into districts, we have noticed that two types of neighbourhoods concentrate the most neweomers : intra muros neighbourhoods with a very dense and mobile population and extra muros neighbourhoods near the coal extraction sites. In all cases, the historical centre of the town, circled off by ancient fortifications, is abandoned. Furthermore, it appears that about half of the immigrants remains less than two years in their first lodgings in Châtelet, while one out of five stays for ten or more years. In following the migrations of these immigrants over three decades until the 1900 census, it can be ascertained that some two thirds left the town- the most often for another industrial township. Among the others remaining in the town, one out of five stayed in the same neighbourhood, even on the same street, two out of five changed neighbourhoods and the two others died. Of the 604 interior migrations of the immigrants over the three decades under observation, 23% took place on the same street, 21% were to another street of the same neighbourhood and 56% to another neighbourhood altogether. In all cases, the "peripheral" districts near the expanding coal-mines draw the most immigrants, spurred on by certain "informed" investors who hastily build row houses to absorb the town's demographic expansion.