View of the Porta Aurea, Palace of Diocletian; After Charles-Louis Clérisseau; France; Late 18th century; Pen and brown ink, brush and yellow-brown wash, graphite on paper; 25 x 20.3 cm . Cooper Hewitt, Smithsonian Design Museum, New York

In architecture, a recess or space between two vertical supports that is set on a wall without doors or windows.