Lenski focuses on Roman history and particularly the history of the later Roman Empire. He is interested in power relations as these played themselves out at all levels of society, from emperors to slaves. His research ranges broadly across Late Antiquity and includes studies in political, military, social, economic, religious, cultural and art history. His two monographs, on the emperors Valens and Constantine, explore the limits of imperial power in light of reader response theory and life-worlds theory. He has also published extensively on the history of slavery in antiquity and is currently working on a translation of the Visigothic Law Code into English.
- “Violence and the Roman Slave,” in Gareth G. Fagan and Werner Reiss (eds.) The Topography of Violence in the Greco-Roman World (Cambridge, 2016) 275-98.
- “Imperial Legislation and the Donatist Controversy: From Constantine to Honorius,” in R. Miles, ed. The Donatist Schism: Controversy and Contexts. Translated Texts for Historians, Contexts 2 (Liverpool, 2016) 166-219.
- “Peasant and Slave in Late Antique North Africa, c. 100-600 CE,” in R. Lizzi Testa, ed. Late Antiquity in Contemporary Debate (Newcastle: Cambridge Scholars Publishing 2017) 113-55.
- “Il valore dell’editto di Milano,” in R. Macchioro, ed. Costantino a Milano: L’editto e la sua storia (313-2013) (Milan, 2017) 5-58.
Books Authored or Co-Authored
- Failure of Empire: Valens and the Roman State In the Fourth Century AD (University of California Press 2002; paper 2014)
- The Romans: From Village to Empire, second edition (Oxford University Press, 2011) (with M.T. Boatwright, D. Gargola, and R. Talbert)
- A Brief History of the Romans, second edition (Oxford University Press, 2013) (with M.T. Boatwright, D. Gargola, and R. Talbert)
- Constantine and the Cities (University of Pennsylvania Press 2016)
- Constantine and the Cities: Imperial Ideology and Civic Politics (University of Pennsylvania Press 2016)
- The Cambridge Companion to the Age of Constantine (Cambridge University Press 2006; revised edition 2011)
- The Power of Religion in Late Antiquity (Ashgate Press, 2009) (with Andrew Cain)
- Costantino prima e dopo Costantino — Constantine before and after Constantine (Edipuglia, 2012) (with G. Bonamente and R. Lizzi Testa)
- What is a Slave Society? The Practice of Slavery in Global Perspective (Cambridge University Press 2018) (co-edited with Catherine M. Cameron)