 Although he earned his honorific of " The Great " ( " Μέγας " ) from Christian historians long after he had died , he could have claimed the title on his military achievements and victories alone . Besides reuniting the Empire under one emperor , Constantine won major victories over the Franks and Alamanni in 306 – 308 , the Franks again in 313 – 314 , the Goths in 332 and the Sarmatians in 334 . By 336 , Constantine had reoccupied most of the long @-@ lost province of Dacia , which Aurelian had been forced to abandon in 271 . At the time of his death , he was planning a great expedition to end raids on the eastern provinces from the Persian Empire . Serving for a total of almost 31 years ( combining his years as co @-@ ruler and sole ruler ) , he was also the longest serving emperor since Augustus and the second longest serving emperor in Roman history . 
