Sergius (Sergios 54) was a layman and was engaged to be married when he was elected to be archbishop of Ravenna; on assuming office he consecrated his bride-to-be, Euphemia 3, as a deaconess: Agnellus, Lib. Pont. Eccl. Rav. 154 ("Sergius ... iste laicus fuit et sponsam habuit. Quam post[quam] regimen ecclesiae suscepit eam Eufimiam sponsam suam diaconissam cunsecravit et in eodem habitu permansit"). Cf. Duchesne, Lib. Pont. I, p. 483, n. 48, and see Jaffé, 2338 and Codex Carolinus, p. 74. He was informed against to pope Stephen III (II) (Stephanos 8) and threatened with dismissal; after Stephanos 8 died, Sergios 54 reached an accommodation with the next pope, Paul I (Paulos 49), and kept his see. At the Council of Rome in 769 it was alleged by Konstantinos 140 (the antipope Constantine) that Sergios 54 was a layman when he was elected as archbishop ("dicens quia et Sergius archiepiscopus Ravennantium laicus existens archiepiscopus effectus est"); when he made the claim, Konstantinos 140 was set upon by the assembled bishops and driven out: Lib. Pont. 96. 19.

In 769 Sergios 54 was represented at the Council of Rome by Valentinus 3 and Ioannes 237: Lib. Pont. 96. 17. The text gives the name of the archbishop as Leo ("presentantes locum domno Leone archiepiscopo civitate Ravennate"), but Sergios 54 was still alive in 769. They are named first in the list of the bishops and clergy from Italy. According to a note in another manuscript of the Liber Pontificalis, two bishops from Flaminian sees, Antoninos 3 and Ioannes 238, were sent to the Council by Sergios 54 ("missis a praedicto Sergio archiepiscopo Ravennae"): Duchesne, Lib. Pont. I, p. 483, n. 44. He died on 25 August 769; see Duchesne, Lib. Pont. III, p. 105, note on Vol. I, p. 484. His death took place a little while after the Council of Rome of 769: Lib. Pont. 96. 25 ("contigit post aliquantum temporis de hac vita migrasse Sergium archiepiscopum civitatis Ravennantium"). For his successors, see Michael 54 and Leo 114.

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