Which god gained popularity among Roman soldiers and was brought from Eastern campaigns?

Mithras gained significant popularity among Roman soldiers for several reasons. He was a deity associated with the mysteries and was particularly appealing to soldiers due to his connections with strength, military success, and the protection of warriors. The cult of Mithras originated in Persia, and as Roman legions expanded into the East, soldiers encountered this religion and brought it back to Rome.

Mithras was often depicted slaying a bull, an act symbolizing the triumph of life over death and regeneration, which resonated with the soldiers facing the perils of military life. The Mithraic mysteries provided a sense of brotherhood, secrecy, and communal participation, which were appealing traits for men serving in a disciplined and often dangerous environment.

The other choices do have their significance in Roman culture but did not gain the same level of traction among soldiers. Magna Mater, or Cybele, was indeed worshipped and significant but was associated more with concepts of fertility and the earth. Lemuria was a festival concerned with appeasing spirits of the dead, and while it dealt with important aspects of Roman life, it lacked direct military connections. Isis, though a popular goddess from Egypt also embraced by Roman citizens, did not have the same strong association with the military as Mithras did