Heraldry is the art and science of designing and using a coat of arms. The study of coats of arms is also called "armory". The practice of using distinct markings on a person's shield started in the Middle Ages, when a knight's helmet covered his face, making everybody look the same in battle. At first, only knights and nobility had coats of arms, but in the Middle Ages, some cities started using heraldry too. By the end of the Middle Ages, other people began using coats of arms, now called "burgher arms", which means they belong to a commoner and not a member of the nobility. An official in charge of approving and recording coats of arms is called a "herald". The related study of flags is called "vexillology".