The Insertion of the Filioque into the Nicene Creed and a Letter of Isidore of Seville
Shawn C. Smith
The common tradition says the filioque first appeared in Nicene Creed at Third Council of Toledo 589. In contrast, manuscript evidence indicates it Eighth 653. date insertion can be narrowed further based on a letter Isidore Seville (d. 636). This (ep. 6) has been typically considered spurious, but supports its authenticity.
Journal of Early Christian Studies