Jewellery shaped like a shield is a fairly common item. You will find lockets, pendants, rings and locks for bracelets which are shield shaped. The meaning of the word ‘shield’ is something that provides protection or defence. A more technical meaning is that it is a piece of metal or other material such as wood, carried, often on the left arm, to protect the front of the body when being attacked. What I want to explore, though, is how the shape of a shield evolved.
The earliest shields that we know about have been found in wall paintings or on pottery, Those of the Ancient Egyptians were roughly rectangular and either oval at the top or tapered to a point. They comprised a wooden frame covered in cowhide. Ancient Greek shields, called Aspis, were generally round, also wood framed and hide covered. The Etruscans followed the Greek style. Ancient Romans had three main shields, the Scutum, the Clipeus and the Parma. The Scutum were large rectangular or oval shields used by foot soldiers. The Clipeus was similar to the Greek Aspis and was round, while the Parma was a small round shield used by the cavalry.
The round shield in various sizes was to remain popular with the Carolingians, Vikings, Anglo-Saxons and so on. From around the 10th century AD, a new shape began to be used – the kite shape. The Normans in particular used this shield shape. The name comes from its similarity to kites (◊). Later, the top of the shield became a straight line, and sometimes there was a peak added to the straight line.
The kite shield developed into the heater-shaped shield in the late medieval period and after. The name was applied to the shield in the Victorian period and refers to the shape of a clothes iron. Variations on the heater shaped shield were developed in heraldry, after the use of shields in battle had ceased.
A good reference on shield shapes is:
George Grazebrook, 'The Dates of Variously-shaped Shields With Coincident Dates and Examples', 1890, https://www.gutenberg.org/files/47761/47761-h/47761-h.htm