The fathers of the Second Ecumenical Council of Constantinople (381) did not intend to define the manner of the Spirit’s procession from the Father, but only to affirm, in language acceptable to the various positions which existed at the time, the full divinity of the Spirit.
The Second Ecumenical Council of Constantinople (381) was not regarded universally as an ecumenical council, especially in the West, until it was declared such by the Fourth Ecumenical Council at Chalcedon (451).
During this time (381-451) there were in the West other forms of the creed, such as The Apostles’. At the same time, there was a tradition coming from the Latin fathers, especially Augustine, which taught the doctrine of the filioque.
Due to distance, cultural difference, language, human error, etc. (historians do not know the exact details), in the 6th century a Latin version of the original creed of Constantinople was published in Spain by the local council of Toledo which added the filioque. It appears that this council considered the filioque clause part of the original. This indicates that such confusion might have been common in the West. Also, it was taken to be an anti-Arian clause, which made it natural, though incorrect, to assume that it was part of the original creed of Constantinople. It is about this time, in both the East and the West that the creed began to be said in the celebration of the Eucharist.
By the 8th century the Carolingian Empire was competing with the Byzantine Empire for its claim to be the true heir to the Roman Imperium in the West. In this context, the filioque (as a doctrine as much as a liturgical addition) had a two-fold function. First, it served the interests of Frankish theologians, especially Alcuin, to condemn what appeared to them to be the heresy of adoptionism in some Spanish churches. Second, it was used by Charlemagne, in his political struggle, to question the orthodoxy of the Byzantine court. It is important to note that, at this time, the filioque clause was added to the original creed of Constantinople in the Frankish dominions but not in those of the Roman See.
Despite Papal support for the theology of the filioque – which had a firm foundation in the Latin fathers – and which was expressed in defense of Western monks in Jerusalem who has been accused by Eastern monks in the early 9th century of heresy for their addition of the filioque to the Latin version of the creed of Constantinople, the filioque clause was deliberately not added to the text of the original Greek or its Latin translation by the Popes of Rome. In fact, the creed itself was introduced into the Mass in Rome not until the 11th century. By that time the Western Empire has passed from the Franks to the Germans and the filioque was added to the original creed of Constantinople in Latin in the Roman rite.
There were two major reunion councils in the medieval period attended by representatives of the Eastern Churches. The first was the Second Council of Lyons (1274). This council was hostile to any view of the origin of the Holy Spirit other than that expressed by the filioque. The second was the Council of Ferrara-Florence. It was attended by representatives from the churches of Constantinople, Alexandria, Antioch, and Jerusalem. It recognized the legitimacy of the Western view of the Spirit’s eternal procession and suggested that the filioque was the same in meaning as certain expressions used by the Greek fathers of the Church in which the Spirit is said to proceed “through the Son.” The decrees of neither of these councils were accepted in the East. The latter council marked the end of serious reunion efforts until the 20th century.