Unlike the Byzantine Empire, the Franks flew a flag before the marriage of Irene and Charlemagne. Known as the Oriflamme, this flag was originally flown by Charlemagne. Following the creation of the Carolingian Union, the Byzantine Empire adopted the Oriflamme, changing it throughout the 9th century.
Before the marriage of Irene of Athens and Charlemagne, the Frankish Empire flew a flag known as the Oriflamme. This banner, adopted by Charlemagne, quickly became synonymous with the Franks following its creation. Its design of a sun surrounded by beams of light led to many other flags of Francia and the Carolingian Empire for centuries after its original conception in the 8th century.
Following the creation of the Carolingian Union by the marriage of Irene of Athens and Charlemagne, the Frankish Oriflamme flown by Charlemagne's men in his many wars was remodeled. Now flying a 'Byzantine shade of purple', this Oriflamme (Oriflamme du Irene) was created to show unity between the Franks and the Byzantines, who shared cold relations at the time of the conception of this union. Flown until 854, the Oriflamme du Irene was used by both the Frankish Empire and Byzantine Empires, albeit with their own changes. The Franks generally left the Oriflamme bare while the Byzantines were keen to place a Chi-Rho above a crossbar holding the Oriflamme.
In 854, the Carolingian Union was embroiled in the First Viking War. Led by Atticus I, the Franks and the Byzantines fought the Vikings out of the Rhine River. Following the bypassing of many traditions involving hereditary rule by Atticus in order to rule both the Franks and the Byzantines, the Oriflamme du Irene was redesigned. Angering the Franks, the Chi-Rho symbol was placed inside the depiction of a sun. The Chi-Rho was a blood red color to symbolize the blood shed during the First Viking Wars. The Oriflamme du Atticus lasted until Constantine VII's rule.
Constantine VII was concerned about Frankish dominance as much as he was afraid of Byzantine dominance. In a bold move, Constantine VII returned the Oriflamme to its red background as opposed to the royal purple background. Retaining the Chi-Rho, the Oriflamme was distinctly Byzantine and Frankish at the same time. The Oriflamme remained this way until Christophorus' decision to change the flag of the Carolingian Empire to a blue background, stating, "We are neither Frankish nor are we Byzantine now."