What is "merena"

Merena was a military officer of the Sassanid Empire during the reign of Shapur II in the 4th century. He was a cavalry commander in the Sassanid army in the course of the Roman-Persian Wars soon after the Battle of Ctesiphon in 363, which took place outside the Sassanid capital Ctesiphon in what is now Iraq. He was among those killed at the subsequent Battle of Samarra, a few hours before the death of the Roman emperor Julian.