In the bustling streets of medieval and early modern London, trust was a precious commodity, just as it is today. But who did Londoner’s choose to trust? And how did the social foundations of trust develop over time? Based on work carried out in a undergraduate research course in the department of economic history at LSE, our paper uncovers a set of previously unrecognized major changes in the sources of trust between people living in London from the 1330s to the 1680s.

Trust is not easily observed, especially in the past, even though it is central to our ideas of social capital, credit and community. Our approach is to look at the kinds of people Londoners were willing to share financial risks with. The risks we study came from looking after money left to orphans by their fathers.

For example, when James Walmesley, a citizen and leatherseller, died in the winter of 1648–9, he left three young sons. It was not until almost twenty years later, in May 1668, that his youngest son, Charles, turned twenty-one and received his share of the £220 estate left by his father. During those decades, Charles and his brothers’ inheritances were held and guaranteed by four individuals acting as “sureties.” Each surety was not just responsible for the money they had in their own hands. Instead, they had pledged to repay the full amount of the Walmesley’s inheritance if the others failed.  Those sureties trusted each other.

Walsmesley’s sureties were one of nearly 15,000 networks established over three centuries to secure orphans’ inheritances. Because we know their name, guild and often their address, the identities of the people who came together in these networks reveal the presence of trusting relationships based on shared guild membership, family ties, or living in the same neighbourhood in the city.

When we look at what connected people, we see a profound shift in the contribution of family and guilds to trust networks among London’s middling and elite classes. This is visible in the graph, which shows what percentage of networks included ties based on guild, family and place in each of the decades we study.

Over time, kinship became increasingly important in creating and reinforcing trust. Families came to play a central role in securing inheritances, re-embedding trust within the family unit.

Shared guild membership, once a significant factor in trust networks, declined in importance. Guilds, which had previously facilitated connections among Londoners, saw their influence wane.

Neighbourhood connections also grew in importance to a high level in the seventeenth century.

The shift in the sources of trust has broader implications for London’s social structure. As kinship bonds strengthened, families became the bedrock of trust networks. Meanwhile, guilds, once powerful mediators of trust and major institutions in shaping city society, receded into the background.

Why did this change occur? We suggest two important developments that overlapped in the sixteenth century were critical. First, the city began to grow rapidly in size. This increased the chance that people had family in the city. Second, the reformation weakened the spiritual and religious role of guilds. Where prayer had been central to medieval guild communities, Henry VIII’s attack on confraternities – local religious societies – stripped away a major source of social connections among guild members.

We chart a transformation in the nature of society in a major European city. London’s trust networks changed significantly over three centuries. Unexpectedly, city growth strengthened the family, while guilds role changed even though they remained strong in other ways. The ways that trust – and society – changed with urban growth are more complex than historians once believed.