The first example is a detailed look at the role of social networks in the rise of the Medici in Florence during the 1400s. The Medici have been called the “godfathers of the Renaissance.” Their accumulation of power in the early fifteenth century in Florence was orchestrated by Cosimo de’ Medici even though his family started with less wealth and political clout than other families in the oligarchy that ruled Florence at the time. Cosimo consolidated political and economic power by leveraging the central position of the Medici in networks of family intermarriages, economic relationships, and political patronage. His understanding of and fortuitous position in these social networks enabled him to build and control an early forerunner to a political party, while other important families of the time floundered in response. Padgett and Ansell 516 provide powerful evidence for this consolidation by documenting the network of marriages between some key families in Florence in the 1430s. Figure 1.1 shows the links between the key families in Florence at that time, where a link represents a marriage between members of two families.1 1. These data were were originally collected by Kent 387, but were first coded by Padgett and Ansell 516, who discuss the network relationships in more detail. The analysis provided here is just a teaser that offers a glimpse of the importance of the network structure. The interested reader should consult Padgett and Ansell 516 for a much richer analysis. 1.2 A Set of Examples 5 During this time the Medici (with Cosimo de’ Medici playing the key role) rose in power and largely consolidated control of business and politics in Florence. Previously Florence had been ruled by an oligarchy of elite families. If one examines wealth and political clout, however, the Medici did not stand out at this time and so one has to look at the structure of social relationships to understand why the Medici rose in power. For instance, the Strozzi had both greater wealth and more seats in the local legislature, and yet the Medici rose to eclipse them. The key to understanding the family’s rise, as Padgett and Ansell 516 detail, can be seen in the network structure. If we do a rough calculation of importance in the network, simply by counting how many families a given family is linked to through marriages, then the Medici do come out on top. However, they only edge out the next highest families, the Strozzi and the Guadagni, by a ratio of 3 to 2. Although suggestive, it is not so dramatic as to be telling. We need to look a bit closer at the network structure to get a better handle on a key to the success of the Medici. In particular, the following measure of betweenness is illuminating.