Unlike his other projects, Gaudí had to work with a limited budget and this explains the use of austere materials, such as brick and reconstituted stone, or the plaster walls inside. However, Gaudí’s genius is evident in the structural system comprising two large skylights and tall, slender parabolic arches which allow natural light to flood the interior hallways. The façade, which also features parabolic arches around the windows, is surmounted by an unusual series of merlons crowned by Saint Teresa’s doctoral biretta. The religious symbology is completed by the turrets at either end of the building, which are surmounted by a four-armed cross.