<Li> Assassination of Aemilianus (253) </Li> <P> Reign of Valerian & Gallienus (253--260) </P> <Ul> <Li> Dura - Europos (256) </Li> <Li> Gothic invasion (256--257) </Li> <Li> Invasion of Shapur (258) </Li> <Li> Invasion of Alamannai (258--260 approx) </Li> <Li> Mediolanum (259) </Li> <Li> Scythian invasion (259--260) </Li> <Li> Edessa (260) </Li> </Ul> <Li> Dura - Europos (256) </Li>

Who did not pose a military threat to the roman empire in the third century