Year 242 (CCXLII) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Gratus and Lepidus (or, less frequently, year 995 Ab urbe condita). The denomination 242 for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
Emperor Gordian III begins a campaign against King Shapur I; Greek philosopher Plotinus joins him, hoping to obtain first-hand knowledge of Persian and Indian philosophies.
Gordian III evacuates the Cimmerian cities in the Bosphorus (Crimea), as the territory is now controlled by the Goths.
Persia
Shapur I makes a pre-emptive attack on Antioch to drive out the Romans. Gordian's father-in-law, Timesitheus, leads a Roman army to defeat the Sassanids at Carrhae and Nisibis.
King Ardashir I, founder of the Sassanid Empire, dies after a 30-year reign. He is succeeded by his son and co-ruler Shapur I.
