council · 809 · Aachen
Charlemagne's theologians at Aachen upheld the Spirit's procession from the Father and the Son and sought Rome's blessing for singing it in the creed. Leo III affirmed the doctrine — and had the creed engraved without the word on silver shields at St Peter's. The West's slow drift on the creed's text continued regardless.
The filioque affirmed at court; Rome agrees in doctrine and declines in text.