Portal is a general term describing an opening in the walls of a building, gate or fortification, and especially a grand entrance to an important structure. Doors, metal gates or portcullis in the opening can be used to control entry or exit. The surface surounding the opening may be made of simple building materials or decorated with ornamentation. The elements of a portal can include the voussoir, tympanum, an ornamented mullion or trumeau between doors, and columns with carvings of saints in the westwork of a church.