Namesakes
Roman and Byzantine Emperors:
3 emperors
Emperor Marcus Flavius Valerius Constantius (a.k.a. Constantius) 305-306 
Emperor Flavius Julius Constantius (a.k.a. Constantius) 337-361
Emperor Flavius Constantius (a.k.a. Constantius) 421
Saints:
2 saints, 1 blessed
Saint Constantius of Perugia ?-170
Saint Constantius ?-520
Blessed Constantius of Fabriano ?-1481