Modern sources put the date of Hatra's fall in 240-241 AD (or April 241 AD) per the newly discovered document Cologne Mani Codex (18.2-8), which is the year that Ardashir I crowned his son Shapur I as the co-regent. Either of these may have conquered Hatra. The siege took one year,[1][2] or two years, according to al-Tabari.[3]