 Diocletian met Maximian in Milan either in late December 290 or January 291 . Crowds gathered to witness the event , and the emperors devoted much time to public pageantry . Potter , among others , has surmised that the ceremonies were arranged to demonstrate Diocletian 's continuing support for his faltering colleague . The rulers discussed matters of politics and war in secret , and they may have considered the idea of expanding the imperial college to include four emperors ( the Tetrarchy ) . Meanwhile , a deputation from the Roman Senate met with the rulers and renewed its infrequent contact with the imperial office . The emperors would not meet again until 303 . 
