Excerpts from Books and Wikipedia
"Jovian (...) was Roman Emperor from 363 to 364. Upon the death of emperor Julian the Apostate during his campaign against the Sassanid Empire, Jovian was hastily declared emperor by his soldiers. He sought peace with the Persians on humiliating terms and reestablished Christianity as the state church. His reign lasted only eight months." [Wikipedia]
"From this point on, Christian emperors would rule the empire. . . . Jovian was a pragmatist. Instead of fighting, he put on his crown and asked Shapur for a parley. He revoked all of Julian’s anti-Christian decrees, but rather than replacing them with equally restrictive decrees against the Roman religion, he declared religious toleration. . . . In 364, eight months after his elevation to the imperial crown, he died in his tent while he was still making his slow way back towards the eastern capital. Reports of the cause were suspiciously varied;" [Bauer: Medieval World, p. 38-40]