Calcified dental plaque (dental calculus) is a source of well-preserved biomolecules, and Warinner et al. now report the high-resolution characterization of the oral microbiome from human dental tissues in four adult human skeletons from approximately AD 950–1200. They identified DNA and proteins from opportunistic pathogens implicated in local and systemic disease as well as DNA sequences with homology to antibiotic resistance genes. They reconstructed the genome from Tannerella forsythensis — a pathogen that has been implicated in periodontal disease. Moreover, the identification of both host and microbial proteins within the dental calculus revealed a long-term role of host immunity and virulence factors in periodontal disease. In addition, biomolecular analysis of plant and animal DNA sequences recovered from the samples provided insights into the medieval human diet.