Final answer:
The smaller shield in the center of a larger shield is known as a boss or umbo, serving to protect the hand and deflect blows.
Step-by-step explanation:
The smaller shield in the center of the larger shield is often referred to as a boss or umbo. This was typically a convex piece covering the handle attachment, and its purpose was to deflect blows from weapons, providing additional protection to the hand. Shields throughout history have varied in design depending upon the civilization and era. The Aztecs, for instance, adorned their shields with intricate patterns and feathers. The Greeks used a meander or Greek key design which carried cultural significance. Medieval knights also utilized shields with central bosses, often richly decorated with their heraldic symbols.