Rio de Janeiro and Buenos Aires, the leading cities of the South Atlantic, experienced substantial growth in wealth holding during the first half of the nineteenth century. In this article, we argue that this growth is best interpreted in a broad, comparative framework, which examines these cities in relation to their internal demographic and institutional arrangements and to their external links to the Atlantic World. Our research emphasizes three major comparative findings. First, according to our samples, both Rio de Janeiro and Buenos Aires experienced substantial growth in wealth holding from the 1820s through the 1850s, well before their participation in the better-known global economic expansion of the late nineteenth century. Second, residents of both South Atlantic cities held wealth broadly similar in scale with their counterparts in comparable cities in North America. And third, wealth inequality was probably no greater in Rio de Janeiro and Buenos Aires than in contemporary cities in the United States. Moreover, we believe that these increases in average wealth holding, as well as changes in the allocation of wealth across sectors, suggests economies that were growing rapidly while becoming more complex.