Complex sentence: The parochial building was first mentioned in records from the eighth century and was originally a baptismal chapel in the imperial palace built by Charlemagne, which the emperor would have visited at Christmas in the year 775.
Split into simpler sentences: The parochial building was first mentioned in records from the eighth century. It is a baptismal chapel in the imperial palace built by Charlemagne, and the emperor would have visited at Christmas in the year 775.