- "The Fall of Rome" series:
- "Centurion" (2010)
- "Praetorian" (2011)
- "Legionary" (2012)
- "Equites" (2013)
- "The Eagle in the Sand" (2014)
- "Blood Eagle" (2015)
- "The Last Legionary" (2016)
- "The Siege of Paris" series:
- "City of Lies" (2018)
- "The Walls of Rome" (2019)
- "Blood River" (2020)
- "Sword of Vengeance" (2021)
- "The Crusader" series:
- "Deus Vult" (2012)
- "Lux Invicta" (2014)
- "Terra Santa" (2016)
- "Saladin's Vengeance" (2018)
- "The Viking Warrior" series:
- "Shield Wall" (2016)
- "God of War" (2017)
- "Warlord" (2018)
- "Blood-Feud" (2019)
- "The Saxon Chronicles" series (co-written with Bernard Cornwell):
- "Sword Song" (2019)
- "War Lord" (2020)
- "Enemy of God" (2021)
Non-fiction:
- "Ancient Rome: A Brief History" (2021)
- "Viking Wars: A Concise History" (2022)