Both periods expressed interpretations of religious ideas, the romanesque used religious and political stability to create massive fortress-like structures as an expression of strength and unity. Whereas in the gothic there was a focus on creating a house of light and an otherworldly experience through verticality and internal illumination. The difference in this religious expression is seen in the thick walls, small apertures, and squat proportions in the Romanesque, compared to the Gothic utilization of flying buttresses, clerestory, spires, and ogival arches, which allow for more light and emphasis the vertical nature of Gothic structures.