Complex sentence: A series of these sunken panels were used as decoration for a ceiling or a vault, also called "caissons", or "lacunaria", while a coffered ceiling was sometime called a "lacunar".
Split into simpler sentences: A series of these sunken panels were used as decoration for a ceiling or a vault. They were also called "caissons", or "lacunaria", while a coffered ceiling was sometime called a "lacunar".