Definition of "mantelshelf"

Sepia Delft tiles surrounded the fireplace, their crudely drawn Biblical scenes in faded cyclamen blending with the pinkish pine, while above them, instead of a mantelshelf, there was an archway high enough to form a balcony with slender balusters and a tapestry-hung wall behind.

1963, Margery Allingham, chapter 3, in The China Governess: A Mystery, London: Chatto & Windus