 Romanos Lekapenos had risen to power in 919 , when he had managed to appoint himself regent over the young Constantine VII and marry his daughter Helena to him . Within a year , he successively rose from basileopator to Caesar , and was eventually crowned senior emperor on 17 December 920 . To consolidate his hold on power , and with a view of supplanting the ruling Macedonian dynasty with his own family , he raised his eldest son Christopher to co @-@ emperor in May 921 , while Stephen and Constantine were proclaimed co @-@ emperors on 25 December 924 . 
