Low Relief, also known as Bas-Relief (from the Italian basso rilievo). Is where the projecting image of a sculpture has a very shallow overall depth. (Read more after Break)
In the lowest types of reliefs, the depth between the respective elements shown is completely distorted, meaning the viewer is deceived as to what the actual depth of the parts is when viewed from straight on, and when seen from the side the human eye is unable to register the image. However, when viewed from the correct viewing position the small variations in depth register as a three-dimensional image to the viewer; despite the sculptures lack of depth, this is achieved through the subtle variations in depth throughout the composition. Which when viewed from the correct angle create the illusion of an image. But when viewed from the wrong angle the viewer is unable to interpret the scene which is being portrayed as all elements would appear distorted, as Low-Relief can only be read from one viewing point.
As a technique Low- Relief requires less work, and therefore cheaper to produce, as less of the surface (background/grounding) is needed to be removed in the carving of the sculpture, therefore less modeling of the key figures is required.
Low Relief was originally prominent during antiquity, however it did experience a revival and resurgence during the Renaissance under artists such as Leon Battista Alberti, Agostino di Duccio and Donatello.