 On 11 November 308 AD , Galerius called a general council at the military city of Carnuntum ( Petronell @-@ Carnuntum , Austria ) to resolve the instability in the western provinces . In attendance were Diocletian , briefly returned from retirement , Galerius , and Maximian . Maximian was forced to abdicate again and Constantine was again demoted to Caesar . Licinius , one of Galerius ' old military companions , was appointed Augustus in the western regions . The new system did not last long : Constantine refused to accept the demotion , and continued to style himself as Augustus on his coinage , even as other members of the Tetrarchy referred to him as a Caesar on theirs . Maximinus Daia was frustrated that he had been passed over for promotion while the newcomer Licinius had been raised to the office of Augustus , and demanded that Galerius promote him . Galerius offered to call both Maximinus and Constantine " sons of the Augusti " , but neither accepted the new title . By the spring of 310 AD , Galerius was referring to both men as Augusti . 
