Namesakes
Bishops of Rome and the Popes:
1 antipope, 1 pope
Constantine (a.k.a. Constantinus) 708-715 
Constantine II (a.k.a. Constantinus) 767-768
Roman and Byzantine Emperors:
12 emperors
Emperor Flavius Valerius Aurelius Constantinus (a.k.a. Constantinus) 306-337
Emperor Flavius Claudius Constantinus (a.k.a. Constantinus) 337-340
Emperor Heraclius Novus Constantinus (a.k.a. Constantinus) 641
Emperor Constantinus Heraclius 641
Emperor Constantinus 668-685
Emperor Constantinus 741-775
Emperor Constantinus 780-797
Emperor Constantinus Porphyrogenitus 913-959
Emperor Constantinus 1025-1028
Emperor Constantinus Monomachus 1042-1055
Emperor Constantinus Ducas 1059-1067
Emperor Constantinus Palaeologus Dragases 1449-1453
Saints:
1 saint
Saint Constantine the Great (a.k.a. Constantinus) c. 272-337