The 809 Council of Aachen defended the creed term Filioque. The Latin word means “and from the Son,” describing the Holy Spirit as proceeding from the Father and the Son.
The clause had become common in parts of the Western Church, especially within the Frankish kingdom. Charlemagne’s court supported its theological use and treated it as an important expression of orthodox belief. The Aachen council was held partly in response to controversy involving Greek-speaking monks in Jerusalem who objected to the Frankish practice of reciting the Creed with Filioque.
The dispute was not simply about translation. Eastern Christian leaders generally preserved the older wording, “from the Father,” while Frankish theologians argued for the expanded Latin form. Pope Leo III accepted the theology but opposed inserting the clause into the Creed itself. He displayed the traditional text in Greek and Latin on silver plaques in Rome.
Rome eventually adopted Filioque in the liturgy in 1014. The controversy later became one of the major theological issues associated with the East–West Schism, although the schism had several political and ecclesiastical causes as well.