A sunken relief is a sculptural technique.
The term relief comes from Latin relevo which means to raise.
Sunk or sunken relief is largely restricted to ancient Egypt, where it became common in the Amarna period ( as opposed to law relief ).
The image is made by cutting the relief sculpture into a flat surface. The figure portrayed is set within a sunken area shaped round the image, so that the relief never rises beyond the original flat surface.
This technique is most successful with strong sunlight as it creates shadows necessary to see the sunken relief.