Relations between the two men deteriorated throughout the year 409, and when Constantine sent an army under his son and heir Constans in the late summer of 410, Gerontius mutinied and installed Maximus.

[1] Kullikowski suggests that Gerontius may have feared being replaced as Constantine's chief military figure in the provinces of Hispania.

[2] Drinkwater on the other hand suggests that Gerontius, seeing Constantine negotiating with Emperor Honorius over 409, had decided to side with the local Theodosian supporters.

However, by the summer of 410 Gerontius had received no support from Italy, was threatened by Constans and desperate for imperial authority to confirm his arrangements with his barbarian allies.

Kullikowski reports that "the mint at Barcino struck coins in his name and there is evidence for major construction work on that city's walls during reign.