* "Makers of the Roman Empire" (2006)
* "Mithras: The Secret God" (2007)
* "The Emperor's New Road: The Power of Rome Across Europe" (2009)
* "Trajan: The Optimus Princeps" (2010)
* "Rome's Quest for the North: Europe Before the Vikings" (2011)
* "The Rise of Christianity: How a Small Sect Grew into a World Religion" (2013)
* "The Oxford Handbook of Roman Studies" (edited, 2014)
* "The Barbarian Empires of the Steppes: From Attila to Kublai Khan" (2017)
* "The Power of Rome: From Republic to Empire" (2018)
* "The Silk Road: A History" (2021)
Articles and Essays
* "The Roman Army and the Punic Wars" (2005)
* "Mithras in the Roman World: A Reappraisal" (2006)
* "The Via Flaminia: Rome's First Great Highway" (2007)
* "Trajan's Column and the Dacian Wars" (2008)
* "The Roman Frontier in Europe: From the Rhine to the Danube" (2009)
* "The Edict of Milan and the Triumph of Christianity" (2010)
* "The Oxford Handbook of Roman Studies: A Review" (2011)
* "The Huns: A New History" (2012)
* "The Visigoths: A History" (2013)
* "The Lombards: A History" (2014)
Other Works
* "The Romans" (2015) (TV documentary series)
* "The Celts" (2016) (TV documentary series)
* "The Vikings" (2017) (TV documentary series)
* "The Silk Road" (2018) (TV documentary series)