 This upper section is called the clerestory.This architectural form is so named because it was commonly used by ancient Roman builders as the structure for secular basilicas used as halls for meetings, markets and as places of justice.Early Christian churches such as Santa Maria Maggiore, Rome, and San Apollinare in Classe have this form, which was adopted by Romanesque builders for their great abbeys and cathedrals, across Europe, such as Durham Cathedral, Abbey of Saint-Étienne, Caen, and Monreale Cathedral.