St Justinian and Symphōnia

Saint Justinian I (c. 482–565 CE), Byzantine emperor from 527 to 565, is one of history’s most influential figures in harmonizing ecclesiastical and imperial authority—a relationship often termed the “symphony” between church and state (from the Greek symphōnia, meaning “agreement” or “concord”). Though the term itself was formalized later (notably in the 6th-century Epanagoge under Basil I), Justinian’s reign laid its practical and legal foundations. His vision was a Christian Roman Empire where emperor and patriarch worked in mutual support: the state enforced orthodoxy, and the church legitimized imperial rule.

Novella 6, Preface (535 CE)
“The two greatest gifts which God, in His infinite goodness, has bestowed upon men from on high are the Priesthood and the Imperium. The former serves divine things; the latter presides over and watches human affairs… If the priesthood is entirely free from fault and possesses confidence before God, and if the emperor governs the state entrusted to him with justice, there will be a good symphony (bona symphonia) between them, and whatever is beneficial will be bestowed upon the human race.”