 On 1 May 305 AD , Diocletian , as a result of a debilitating sickness taken in the winter of 304 – 305 AD , announced his resignation . In a parallel ceremony in Milan , Maximian did the same . Lactantius states that Galerius manipulated the weakened Diocletian into resigning , and forced him to accept Galerius ' allies in the imperial succession . According to Lactantius , the crowd listening to Diocletian 's resignation speech believed , until the very last moment , that Diocletian would choose Constantine and Maxentius ( Maximian 's son ) as his successors . It was not to be : Constantius and Galerius were promoted to Augusti , while Severus and Maximinus Daia , Galerius ' nephew , were appointed their Caesars respectively . Constantine and Maxentius were ignored . 
