Tiaras, crowns, circlets and diadems have always been used by royalty to show their position in the world.
Wikipedia says: "A diadem is type of crown, specifically an ornamental headband worn by Eastern monarchs and others as a badge of royalty. The word derives from the Greek διάδημα diádēma, "band" or "fillet", from διαδέω diadéō, "I bind round", or "I fasten".
The term originally referred to the embroidered white silk ribbon, ending in a knot and two fringed strips often draped over the shoulders, that surrounded the head of the king to denote his authority. Such ribbons were also used to crown victorious athletes in important sports games in antiquity. It was later applied to a metal crown, generally in a circular or "fillet" shape. For example, the crown worn by the kings of Anglo-Saxon England was a diadem, as was that of a baron later (in some countries surmounted by three globes). The ancient Celts were believed to have used a thin, semioval gold plate called a mind (Old Irish) as a diadem. Some of the earliest examples of these types of crowns can be found in ancient Egypt, from the simple fabric type to the more elaborate metallic type, and in the Aegean world.."
So now you know! We just love the way these crowns and diadems make every bride look as beautiful and regal as a queen.
So it really doesn't matter if you can tell the difference between a crown, a diadem or a circlet, as long as you feel beautiful in it on your wedding day that's all that matters!