Constantine (Greek: Κωνσταντῖνος; born between 855 and c. 865, died 3 September 879) was a junior Byzantine emperor, alongside Basil I as the senior emperor, from January 868 to 3 September 879. His parentage is a matter of debate, but he is generally assumed to be the son of Byzantine Emperor Basil I (r. 867–886) and his first wife, or second wife Eudokia Ingerina; although other theories include him being the son of Emperor Michael III (r. 842–867) and Eudokia. Constantine was made co-emperor by his father in c. January 868. He was engaged to Ermengard of Italy, the daughter of Holy Roman Emperor Louis II, in 870/871, but it is not known if he ever married her; some sources take the affirmative stance, while others argue there is no concrete evidence. As emperor, he served in several ca