Eduard Meyer,
1911 Encyclopædia Britannica, Volume 24…
(1911)
“ In 337, just before the death of Constantine, Shapur broke the peace concluded in 297 between Narses and Diocletian, which had been observed for forty years, and a war of twenty-six years (337–363) began (Shapur attempted with varying success to conquer the great fortresses of Roman Mesopotamia, Singara, Nisibis (which he invested three times in vain) , Amida (Diarbekr) . The emperor Constantius II. was always beaten in the field. Nevertheless Shapur made scarcely any progress; the military power of his kingdom was not sufficient for a lasting occupation of the conquered districts. ”
