A number of significant councils of the Roman Catholic Church were held at Aachen in the early Middle Ages.

In the mixed council of 798, Charlemagne proclaimed a capitulary of eighty-one chapters, largely a repetition of earlier ecclesiastical legislation, that was accepted by the clergy and acquired canonical authority. At the council of 799, after a discussion of six days Felix, Bishop of Urgel in Spain, avowed himself overcome by Alcuin and withdrew his theory of Adoptianism.

The council that was held in 809 is generally thought that to have initiated what is now known as the filioque dispute.^{[citation needed]}

In the synods of 816, 817, 818, and 819, clerical and monastic discipline was the chief issue, and the Regula Aquensis was made obligatory on all establishments of canons and canonesses, while a new revision of the Rule of St. Benedict was imposed on the monks of the Benedictine Order by Benedict of Aniane. The synod of 836 was largely attended and devoted itself to the restoration of ecclesiastical discipline that had been affected by the civil wars between Louis the Pious and his sons.

From 860 to 862 three councils were occupied with the question of the divorce of King Lothaire I from his wife, Theutberga.

In 1166 took place the schismatic council, approved by the Antipope Paschal III, in which was decreed the canonization of Charlemagne, that was solemnly celebrated 29 December of that year.

This article incorporates text from the entry Aachen in the public-domain Catholic Encyclopedia of 1913.

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