Hairan I was apparently elevated to co-lordship by his father, as an inscription from 251 testifies. As early as the 240s, Odaenathus bolstered the Palmyrene army, recruiting desert nomads and increasing the number of the Palmyrene heavy cavalry (clibanarii). In 252, the Persian emperor, Shapur I, started a full-scale invasion of the Roman provinces in the east. During the second campaign of the invasion, Shapur I conquered Antioch on the Orontes, the traditional capital of Syria, and headed south, where his advance was checked in 253 by a noble from Emesa, Uranius Antoninus. The events of 253 were mentioned in the works of the sixth-century historian John Malalas who also mentioned a leader by the name "Enathus" inflicting a defeat upon the retreating Shapur I near the Euphrates. "Enathus" is probably identical with Odaenathus, and while Malalas' account indicates that Odaenathus defeated the Persians in 253, there is no proof that the Palmyrene leader engaged Shapur I before 260 and Malalas' account seems to be confusing Odaenathus' future actions during 260 with the events of 253.