Roman diplomas were folded metal plates that proved you could travel.
The word diploma comes from the Greek diplōma, meaning a document folded in two, from diploun, to double or fold.1 In the Roman Empire, a diploma was a bronze certificate issued to soldiers upon their discharge, confirming their service and granting privileges such as citizenship and the right of legal marriage. Two thin bronze plates were bound together and sealed, creating a folded document that served as proof of identity and status.2
The document was a passport, a credential, and a contract in one.
By the medieval period, diploma had shifted its meaning to refer to official documents issued by sovereigns and ecclesiastical authorities. Universities adopted the term for the certificates they granted to graduates. The University of Bologna, founded around 1088, and the University of Paris, established around 1150, were among the earliest institutions to formalize the granting of degrees.3
The assumption that a paper document could certify a person's competence became one of the foundational ideas of the modern labor market.
The credential system expanded dramatically in the twentieth century. In the United States, the percentage of adults holding a bachelor's degree rose from roughly five percent in 1940 to over thirty-seven percent by 2022.4 Employers who once hired on the basis of skill or apprenticeship increasingly required diplomas as a prerequisite for employment, a phenomenon economists call credential inflation.5
The Roman soldier's bronze plates proved that he had served. The modern diploma proves that someone attended. Whether it proves competence remains an open question in the labor market.