Einhard. The Life of the Emperor Charles. Chapter 26.
He cherished with the greatest fervor and devotion the principles of the Christian religion, which had been instilled into him from infancy. Hence it was that he built the beautiful basilica at Aix-la-Chapelle, which he adorned with gold and silver and lamps, and with rails and doors of solid brass. He had the columns and marbles for this structure brought from Rome and Ravenna, for he could not find such as were suitable elsewhere. He was a constant worshipper at this church as long as his health permitted, going morning and evening, even after nightfall, besides attending mass; and he took care that all the services there conducted should be administered with the utmost possible propriety, very often warning the sextons not to let any improper or unclean thing be brought into the building or remain in it. He provided it with a great number of sacred vessels of gold and silver and with such a quantity of clerical robes that not even the doorkeepers who fill the humblest office in the church were obliged to wear their everyday clothes when in the exercise of their duties. He was at great pains to improve the church reading and psalmody, for he was well skilled in both, although he neither read in public nor sang, except in a low tone and with others.