The custom of wearing wedding rings on the left hand originated in the third century B.C. in Greece. Physicians of that time incorrectly believed that a vein in the third finger of the left hand ran directly into the heart. Therefore, it made compelling sense that this body part should be chosen to bear a symbol of eternal love. The vein was known as "Vena Amoris," the "Vein of Love."
Having no scientific interpretation of their own, the Romans eventually adopted the Greeks' ring custom. Rather than offering rings as a token of love, they were made of iron and awarded to women as symbols of ownership.
In the 12th century, Pope Innocent III declared that marriages must take place in a Catholic church and the ceremony must include the giving of rings. In the 16th century, England's monarch, King Edward the VI, mandated that the left hand be called "the marriage hand" since the heart is located on the left side of the body.
Throughout history, wedding rings have been worn on different fingers, including the thumb, on both the left and right hand. However, it was thought that wearing a ring on the left hand helped prevent injury when performing physical labor, since most people were right-handed.